Convert Mono.Linker.Tests from MSTest to xUnit

[Copilot]

Description

Converts Mono.Linker.Tests — the last remaining MSTest project in illink — to xUnit, aligning it with the rest of dotnet/runtime's test infrastructure.

Changes

Project setup

• Remove <TestRunnerName>MSTest</TestRunnerName> from csproj; xUnit is now the default via Arcade
• Add explicit Microsoft.DotNet.XUnitExtensions PackageReference (not auto-imported for src/tools/illink/)

Test data / dynamic data

• TestDatabase: return types changed from IEnumerable<TestDataRow<TestCase>> → IEnumerable<object[]>; MSTestCasesBySuiteName → TestCasesBySuiteName
• MemberAssertionsCollector.GetMemberAssertionsData: returns IEnumerable<object[]> instead of IEnumerable<TestDataRow<T>>
• TestCase.ToString() added to emit DisplayName for readable xUnit test names
• [DynamicData(..., new object[] { typeof(T) })] with parameterized data source → parameterless [MemberData] method per test class

Test attributes

• [TestClass] removed; [TestMethod] → [Fact]; [DataRow] → [InlineData]
• [DynamicData] → [MemberData]; suite tests use [ConditionalTheory] (not plain [Theory]) to support dynamic skipping
• [TestInitialize] → constructor; [DoNotParallelize] removed (MSTest-only concept)
• AssemblyInfo.cs parallel configuration removed

Dynamic skipping
MSTest's Assert.Inconclusive doesn't translate directly to xUnit's skip mechanism. Most runtime skipping uses ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions. For CodegenAnnotationTests, declarative [SkipOnTargetFramework] attributes are used instead:

// Before (MSTest)if(Environment.OSVersion.Platform==PlatformID.Win32NT)Assert.Inconclusive("These tests are not valid when trimming .NET Framework");
#if NETAssert.Inconclusive("These tests are not valid when trimming .NET Core");
#endif
// After (xUnit)[SkipOnTargetFramework(TargetFrameworkMonikers.Netcoreapp,"These tests are not valid when trimming .NET Core")][SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework,"These tests are not valid when trimming .NET Framework")]

The [SkipOnTargetFramework] attribute adds a Category=Failing trait via SkipOnTargetFrameworkDiscoverer, which is automatically filtered out by the CI infrastructure via _withoutCategories=failing in eng/testing/tests.targets.

Assertions (all files)

MSTest	xUnit
Assert.AreEqual(a, b)	Assert.Equal(a, b)
Assert.IsTrue/IsFalse	Assert.True/False
Assert.IsNull/IsNotNull	Assert.Null/NotNull → Assert.True(x is not null, $"...") with diagnostic message
Assert.IsEmpty	Assert.Empty / Assert.True(x.Length == 0, message)
Assert.Inconclusive	throw new SkipTestException
CollectionAssert.AreEquivalent	Assert.Equal(expected.OrderBy(...), actual.OrderBy(...))
UnitTestAssertException	XunitException

Assertion quality fixes

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") to preserve diagnostic context; changed Single(...) → SingleOrDefault(...) so the null check is actually reachable and surfaces the descriptive message on failure
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") replacing the redundant Assert.NotNull
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes linker output when exit codes don't match
• ResultChecker.cs:834-835: corrected Assert.Equal argument order so expected is first and actual is second, producing correct diff output on failure
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, ...) including the linked assembly name and missing type list
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, ...) including the type name and missing member names
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines in the failure message
• TestFrameworkRulesAndConventions.cs:42: replaced Assert.Empty(missing) with Assert.True(missing.Length == 0, $"Could not find a test case type for the following source file(s): ...") to preserve the explanatory failure message
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all MVID assertions

Miscellaneous fixes

• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit; to prevent CS8019 build warning
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace on blank line

Testing

Build: dotnet build src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Run: dotnet test src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Original prompt

Chronological Review: 1. User requested converting illink tests from MSTest to xUnit 2. Prior work (summarized): Explored repo, found only Mono.Linker.Tests uses MSTest, ran baseline build, delegated bulk conversion to sub-agent (22 files), committed as 9425ffe083f 3. Prior work: Discovered 31 test failures due to dynamic skip mechanism, fixed with ConditionalTheory + SkipTestException (3 files) 4. Prior work: Started code review skill, gathered diff context 5. Current session: Completed code review and amended commit

Recent Commands Analysis:

• Checked AreEqual→Assert.True conversions in ResultChecker.cs diff
• Verified SkipTestException and ConditionalTheory usage in TestSuites.cs
• Found only 1 instance of Assert.True(a == b, msg) pattern at line 259
• Wrote code review (LGTM with one 💡 suggestion about Assert.NotNull message loss)
• Staged 3 uncommitted files and amended commit
• Final commit: 2a2d31b5610
• Called task_complete

Progress: Everything is DONE. The task is complete.

1. Conversation Overview: - Primary Objectives: "Update the illink tests from MSTest to xunit." - Session Context: User requested converting `Mono.Linker.Tests` (the last MSTest test project in illink) to xUnit. Work progressed through exploration → bulk conversion → fixing dynamic skip failures → code review → final commit. - User Intent Evolution: Single clear request, no changes in direction.

2. Technical Foundation:

   • xUnit v2 runner (2.9.x) with xUnit v3 assertions (Microsoft.DotNet.XUnitAssert 3.2.2-beta) — the dotnet/runtime standard setup
   • Arcade SDK: Tests.targets defaults TestRunnerName=XUnit; removing <TestRunnerName>MSTest</TestRunnerName> switches to xUnit packages automatically
   • Microsoft.DotNet.XUnitExtensions: Provides ConditionalTheory/ConditionalFact and SkipTestException for dynamic test skipping. NOT auto-imported for src/tools/illink/ (only for src/libraries/ and src/tests/), so needed explicit PackageReference.
   • SDK version: 11.0.100-preview.3.26170.106

3. Codebase Status:

   • All 22 files committed in single commit 2a2d31b5610 on branch illink-xunit
   • Key files:
     • Mono.Linker.Tests.csproj — Removed TestRunnerName=MSTest, added Microsoft.DotNet.XUnitExtensions PackageReference
     • TestSuites.cs — 47 [ConditionalTheory] methods, [MemberData] instead of [DynamicData], SkipTestException for dynamic skips
     • TestRunner.cs — IgnoreTest throws SkipTestException, catches XunitException instead of UnitTestAssertException
     • TestDatabase.cs — object[] instead of TestDataRow<TestCase>, renamed MSTestCasesBySuiteName → TestCasesBySuiteName
     • TestCase.cs — Added ToString() override returning DisplayName
     • ResultChecker.cs — Dozens of assertion conversions; 3 Assert.NotNull calls lost custom messages; 1 Assert.True(a == b, msg) pattern at line 259
     • 16 other files with attribute/using/assertion conversions

4. Problem Resolution:

   • 31 test failures from dynamic skip: SkipException.ForSkip() (Xunit.Sdk) produces $XunitDynamicSkip$ prefix not caught by xUnit v2 runner. Fixed by using ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions.
   • Assert.NotNull message loss: xUnit's Assert.NotNull doesn't accept messages. Accepted as known tradeoff (3 instances).
   • Assert.AreEqual with message: One instance converted to Assert.True(a == b, msg) to preserve diagnostic output including linker output.

5. Progress Tracking:

   • ✅ Baseline build succeeded
   • ✅ All 22 files converted from MSTest to xUnit
   • ✅ Dynamic skip mechanism fixed (ConditionalTheory + SkipTestException)
   • ✅ Build passes (0 errors, 0 warnings)
   • ✅ Tests pass: 0 Failed, 1125 Passed, 31 Skipped
   • ✅ Code review completed (LGTM, one 💡 suggestion)
   • ✅ All changes committed in single amended commit 2a2d31b5610
   • ✅ task_complete called

6. Active Work State:

   • Task is COMPLETE.task_complete was called with full summary.

7. Recent Operations:

   • Last Agent Commands:
     1. bash: git diff HEAD~1 -- ResultChecker.cs | grep "Assert.AreEqual.*Assert.True" — no results
     2. bash: git diff HEAD~1 -- ResultChecker.cs | grep -A1 "Assert.AreEqual" — found the 3 AreEqual conversions including the Assert.True pattern
     3. bash: grep "Assert.True.*==\|Assert.False.*!=" ResultChecker.cs — confirmed only 1 instance at line 259
     4. bash: grep "SkipTestException" TestSuites.cs — confirmed 2 usages
     5. Wrote code review output (LGTM with findings)
     6. bash: git add -A && git diff --cached --stat — staged 3 files (csproj, TestSuites.cs, TestRunner.cs)
     7. bash: git commit --amend — amended commit to 2a2d31b5610 with 22 files, 369 insertions, 396 deletions
     8. bash: git log --oneline -2 — verified commit on illink-xunit branch
     9. `ta...

Created from Copilot CLI via the copilot delegate command.

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @dotnet/illink
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 7 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in b0154e0:

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") with descriptive messages
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes the linker output
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all three MVID assertions
• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit;
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 4 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in d5455d5:

• ResultChecker.cs:73: changed Single(...) → SingleOrDefault(...) so the subsequent Assert.True(assemblyRef is not null, ...) is reachable and shows the helpful message
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") with context replacing the redundant Assert.NotNull
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, $"Missing types in linked assembly '{...}': ...")
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, $"Missing members in type '{...}' in linked assembly '{...}': ...")

[Copilot]

Description

Converts Mono.Linker.Tests — the last remaining MSTest project in illink — to xUnit, aligning it with the rest of dotnet/runtime's test infrastructure.

Changes

Project setup

• Remove <TestRunnerName>MSTest</TestRunnerName> from csproj; xUnit is now the default via Arcade
• Add explicit Microsoft.DotNet.XUnitExtensions PackageReference (not auto-imported for src/tools/illink/)

Test data / dynamic data

• TestDatabase: return types changed from IEnumerable<TestDataRow<TestCase>> → IEnumerable<object[]>; MSTestCasesBySuiteName → TestCasesBySuiteName
• MemberAssertionsCollector.GetMemberAssertionsData: returns IEnumerable<object[]> instead of IEnumerable<TestDataRow<T>>
• TestCase.ToString() added to emit DisplayName for readable xUnit test names
• [DynamicData(..., new object[] { typeof(T) })] with parameterized data source → parameterless [MemberData] method per test class

Test attributes

• [TestClass] removed; [TestMethod] → [Fact]; [DataRow] → [InlineData]
• [DynamicData] → [MemberData]; suite tests use [ConditionalTheory] (not plain [Theory]) to support dynamic skipping
• [TestInitialize] → constructor; [DoNotParallelize] removed (MSTest-only concept)
• AssemblyInfo.cs parallel configuration removed

Dynamic skipping
MSTest's Assert.Inconclusive doesn't translate directly to xUnit's skip mechanism. Most runtime skipping uses ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions. For CodegenAnnotationTests, declarative [SkipOnTargetFramework] attributes are used instead:

// Before (MSTest)if(Environment.OSVersion.Platform==PlatformID.Win32NT)Assert.Inconclusive("These tests are not valid when trimming .NET Framework");
#if NETAssert.Inconclusive("These tests are not valid when trimming .NET Core");
#endif
// After (xUnit)[SkipOnTargetFramework(TargetFrameworkMonikers.Netcoreapp,"These tests are not valid when trimming .NET Core")][SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework,"These tests are not valid when trimming .NET Framework")]

The [SkipOnTargetFramework] attribute adds a Category=Failing trait via SkipOnTargetFrameworkDiscoverer, which is automatically filtered out by the CI infrastructure via _withoutCategories=failing in eng/testing/tests.targets.

Assertions (all files)

MSTest	xUnit
Assert.AreEqual(a, b)	Assert.Equal(a, b)
Assert.IsTrue/IsFalse	Assert.True/False
Assert.IsNull/IsNotNull	Assert.Null/NotNull → Assert.True(x is not null, $"...") with diagnostic message
Assert.IsEmpty	Assert.Empty / Assert.True(x.Length == 0, message)
Assert.Inconclusive	throw new SkipTestException
CollectionAssert.AreEquivalent	Assert.Equal(expected.OrderBy(...), actual.OrderBy(...))
UnitTestAssertException	XunitException

Assertion quality fixes

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") to preserve diagnostic context; changed Single(...) → SingleOrDefault(...) so the null check is actually reachable and surfaces the descriptive message on failure
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") replacing the redundant Assert.NotNull
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes linker output when exit codes don't match
• ResultChecker.cs:834-835: corrected Assert.Equal argument order so expected is first and actual is second, producing correct diff output on failure
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, ...) including the linked assembly name and missing type list
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, ...) including the type name and missing member names
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines in the failure message
• TestFrameworkRulesAndConventions.cs:42: replaced Assert.Empty(missing) with Assert.True(missing.Length == 0, $"Could not find a test case type for the following source file(s): ...") to preserve the explanatory failure message
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all MVID assertions

Miscellaneous fixes

• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit; to prevent CS8019 build warning
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace on blank line

Testing

Build: dotnet build src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Run: dotnet test src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Original prompt

Chronological Review: 1. User requested converting illink tests from MSTest to xUnit 2. Prior work (summarized): Explored repo, found only Mono.Linker.Tests uses MSTest, ran baseline build, delegated bulk conversion to sub-agent (22 files), committed as 9425ffe083f 3. Prior work: Discovered 31 test failures due to dynamic skip mechanism, fixed with ConditionalTheory + SkipTestException (3 files) 4. Prior work: Started code review skill, gathered diff context 5. Current session: Completed code review and amended commit

Recent Commands Analysis:

• Checked AreEqual→Assert.True conversions in ResultChecker.cs diff
• Verified SkipTestException and ConditionalTheory usage in TestSuites.cs
• Found only 1 instance of Assert.True(a == b, msg) pattern at line 259
• Wrote code review (LGTM with one 💡 suggestion about Assert.NotNull message loss)
• Staged 3 uncommitted files and amended commit
• Final commit: 2a2d31b5610
• Called task_complete

Progress: Everything is DONE. The task is complete.

1. Conversation Overview: - Primary Objectives: "Update the illink tests from MSTest to xunit." - Session Context: User requested converting `Mono.Linker.Tests` (the last MSTest test project in illink) to xUnit. Work progressed through exploration → bulk conversion → fixing dynamic skip failures → code review → final commit. - User Intent Evolution: Single clear request, no changes in direction.

2. Technical Foundation:

   • xUnit v2 runner (2.9.x) with xUnit v3 assertions (Microsoft.DotNet.XUnitAssert 3.2.2-beta) — the dotnet/runtime standard setup
   • Arcade SDK: Tests.targets defaults TestRunnerName=XUnit; removing <TestRunnerName>MSTest</TestRunnerName> switches to xUnit packages automatically
   • Microsoft.DotNet.XUnitExtensions: Provides ConditionalTheory/ConditionalFact and SkipTestException for dynamic test skipping. NOT auto-imported for src/tools/illink/ (only for src/libraries/ and src/tests/), so needed explicit PackageReference.
   • SDK version: 11.0.100-preview.3.26170.106

3. Codebase Status:

   • All 22 files committed in single commit 2a2d31b5610 on branch illink-xunit
   • Key files:
     • Mono.Linker.Tests.csproj — Removed TestRunnerName=MSTest, added Microsoft.DotNet.XUnitExtensions PackageReference
     • TestSuites.cs — 47 [ConditionalTheory] methods, [MemberData] instead of [DynamicData], SkipTestException for dynamic skips
     • TestRunner.cs — IgnoreTest throws SkipTestException, catches XunitException instead of UnitTestAssertException
     • TestDatabase.cs — object[] instead of TestDataRow<TestCase>, renamed MSTestCasesBySuiteName → TestCasesBySuiteName
     • TestCase.cs — Added ToString() override returning DisplayName
     • ResultChecker.cs — Dozens of assertion conversions; 3 Assert.NotNull calls lost custom messages; 1 Assert.True(a == b, msg) pattern at line 259
     • 16 other files with attribute/using/assertion conversions

4. Problem Resolution:

   • 31 test failures from dynamic skip: SkipException.ForSkip() (Xunit.Sdk) produces $XunitDynamicSkip$ prefix not caught by xUnit v2 runner. Fixed by using ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions.
   • Assert.NotNull message loss: xUnit's Assert.NotNull doesn't accept messages. Accepted as known tradeoff (3 instances).
   • Assert.AreEqual with message: One instance converted to Assert.True(a == b, msg) to preserve diagnostic output including linker output.

5. Progress Tracking:

   • ✅ Baseline build succeeded
   • ✅ All 22 files converted from MSTest to xUnit
   • ✅ Dynamic skip mechanism fixed (ConditionalTheory + SkipTestException)
   • ✅ Build passes (0 errors, 0 warnings)
   • ✅ Tests pass: 0 Failed, 1125 Passed, 31 Skipped
   • ✅ Code review completed (LGTM, one 💡 suggestion)
   • ✅ All changes committed in single amended commit 2a2d31b5610
   • ✅ task_complete called

6. Active Work State:

   • Task is COMPLETE.task_complete was called with full summary.

7. Recent Operations:

   • Last Agent Commands:
     1. bash: git diff HEAD~1 -- ResultChecker.cs | grep "Assert.AreEqual.*Assert.True" — no results
     2. bash: git diff HEAD~1 -- ResultChecker.cs | grep -A1 "Assert.AreEqual" — found the 3 AreEqual conversions including the Assert.True pattern
     3. bash: grep "Assert.True.*==\|Assert.False.*!=" ResultChecker.cs — confirmed only 1 instance at line 259
     4. bash: grep "SkipTestException" TestSuites.cs — confirmed 2 usages
     5. Wrote code review output (LGTM with findings)
     6. bash: git add -A && git diff --cached --stat — staged 3 files (csproj, TestSuites.cs, TestRunner.cs)
     7. bash: git commit --amend — amended commit to 2a2d31b5610 with 22 files, 369 insertions, 396 deletions
     8. bash: git log --oneline -2 — verified commit on illink-xunit branch
     9. `ta...

Created from Copilot CLI via the copilot delegate command.

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @dotnet/illink
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 7 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in b0154e0:

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") with descriptive messages
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes the linker output
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all three MVID assertions
• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit;
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 4 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in d5455d5:

• ResultChecker.cs:73: changed Single(...) → SingleOrDefault(...) so the subsequent Assert.True(assemblyRef is not null, ...) is reachable and shows the helpful message
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") with context replacing the redundant Assert.NotNull
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, $"Missing types in linked assembly '{...}': ...")
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, $"Missing members in type '{...}' in linked assembly '{...}': ...")

[Copilot]

Description

Converts Mono.Linker.Tests — the last remaining MSTest project in illink — to xUnit, aligning it with the rest of dotnet/runtime's test infrastructure.

Changes

Project setup

• Remove <TestRunnerName>MSTest</TestRunnerName> from csproj; xUnit is now the default via Arcade
• Add explicit Microsoft.DotNet.XUnitExtensions PackageReference (not auto-imported for src/tools/illink/)

Test data / dynamic data

• TestDatabase: return types changed from IEnumerable<TestDataRow<TestCase>> → IEnumerable<object[]>; MSTestCasesBySuiteName → TestCasesBySuiteName
• MemberAssertionsCollector.GetMemberAssertionsData: returns IEnumerable<object[]> instead of IEnumerable<TestDataRow<T>>
• TestCase.ToString() added to emit DisplayName for readable xUnit test names
• [DynamicData(..., new object[] { typeof(T) })] with parameterized data source → parameterless [MemberData] method per test class

Test attributes

• [TestClass] removed; [TestMethod] → [Fact]; [DataRow] → [InlineData]
• [DynamicData] → [MemberData]; suite tests use [ConditionalTheory] (not plain [Theory]) to support dynamic skipping
• [TestInitialize] → constructor; [DoNotParallelize] removed (MSTest-only concept)
• AssemblyInfo.cs parallel configuration removed

Dynamic skipping
MSTest's Assert.Inconclusive doesn't translate directly to xUnit's skip mechanism. Most runtime skipping uses ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions. For CodegenAnnotationTests, declarative [SkipOnTargetFramework] attributes are used instead:

// Before (MSTest)if(Environment.OSVersion.Platform==PlatformID.Win32NT)Assert.Inconclusive("These tests are not valid when trimming .NET Framework");
#if NETAssert.Inconclusive("These tests are not valid when trimming .NET Core");
#endif
// After (xUnit)[SkipOnTargetFramework(TargetFrameworkMonikers.Netcoreapp,"These tests are not valid when trimming .NET Core")][SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework,"These tests are not valid when trimming .NET Framework")]

The [SkipOnTargetFramework] attribute adds a Category=Failing trait via SkipOnTargetFrameworkDiscoverer, which is automatically filtered out by the CI infrastructure via _withoutCategories=failing in eng/testing/tests.targets.

Assertions (all files)

MSTest	xUnit
Assert.AreEqual(a, b)	Assert.Equal(a, b)
Assert.IsTrue/IsFalse	Assert.True/False
Assert.IsNull/IsNotNull	Assert.Null/NotNull → Assert.True(x is not null, $"...") with diagnostic message
Assert.IsEmpty	Assert.Empty / Assert.True(x.Length == 0, message)
Assert.Inconclusive	throw new SkipTestException
CollectionAssert.AreEquivalent	Assert.Equal(expected.OrderBy(...), actual.OrderBy(...))
UnitTestAssertException	XunitException

Assertion quality fixes

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") to preserve diagnostic context; changed Single(...) → SingleOrDefault(...) so the null check is actually reachable and surfaces the descriptive message on failure
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") replacing the redundant Assert.NotNull
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes linker output when exit codes don't match
• ResultChecker.cs:834-835: corrected Assert.Equal argument order so expected is first and actual is second, producing correct diff output on failure
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, ...) including the linked assembly name and missing type list
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, ...) including the type name and missing member names
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines in the failure message
• TestFrameworkRulesAndConventions.cs:42: replaced Assert.Empty(missing) with Assert.True(missing.Length == 0, $"Could not find a test case type for the following source file(s): ...") to preserve the explanatory failure message
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all MVID assertions

Miscellaneous fixes

• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit; to prevent CS8019 build warning
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace on blank line

Testing

Build: dotnet build src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Run: dotnet test src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Original prompt

Chronological Review: 1. User requested converting illink tests from MSTest to xUnit 2. Prior work (summarized): Explored repo, found only Mono.Linker.Tests uses MSTest, ran baseline build, delegated bulk conversion to sub-agent (22 files), committed as 9425ffe083f 3. Prior work: Discovered 31 test failures due to dynamic skip mechanism, fixed with ConditionalTheory + SkipTestException (3 files) 4. Prior work: Started code review skill, gathered diff context 5. Current session: Completed code review and amended commit

Recent Commands Analysis:

• Checked AreEqual→Assert.True conversions in ResultChecker.cs diff
• Verified SkipTestException and ConditionalTheory usage in TestSuites.cs
• Found only 1 instance of Assert.True(a == b, msg) pattern at line 259
• Wrote code review (LGTM with one 💡 suggestion about Assert.NotNull message loss)
• Staged 3 uncommitted files and amended commit
• Final commit: 2a2d31b5610
• Called task_complete

Progress: Everything is DONE. The task is complete.

1. Conversation Overview: - Primary Objectives: "Update the illink tests from MSTest to xunit." - Session Context: User requested converting `Mono.Linker.Tests` (the last MSTest test project in illink) to xUnit. Work progressed through exploration → bulk conversion → fixing dynamic skip failures → code review → final commit. - User Intent Evolution: Single clear request, no changes in direction.

2. Technical Foundation:

   • xUnit v2 runner (2.9.x) with xUnit v3 assertions (Microsoft.DotNet.XUnitAssert 3.2.2-beta) — the dotnet/runtime standard setup
   • Arcade SDK: Tests.targets defaults TestRunnerName=XUnit; removing <TestRunnerName>MSTest</TestRunnerName> switches to xUnit packages automatically
   • Microsoft.DotNet.XUnitExtensions: Provides ConditionalTheory/ConditionalFact and SkipTestException for dynamic test skipping. NOT auto-imported for src/tools/illink/ (only for src/libraries/ and src/tests/), so needed explicit PackageReference.
   • SDK version: 11.0.100-preview.3.26170.106

3. Codebase Status:

   • All 22 files committed in single commit 2a2d31b5610 on branch illink-xunit
   • Key files:
     • Mono.Linker.Tests.csproj — Removed TestRunnerName=MSTest, added Microsoft.DotNet.XUnitExtensions PackageReference
     • TestSuites.cs — 47 [ConditionalTheory] methods, [MemberData] instead of [DynamicData], SkipTestException for dynamic skips
     • TestRunner.cs — IgnoreTest throws SkipTestException, catches XunitException instead of UnitTestAssertException
     • TestDatabase.cs — object[] instead of TestDataRow<TestCase>, renamed MSTestCasesBySuiteName → TestCasesBySuiteName
     • TestCase.cs — Added ToString() override returning DisplayName
     • ResultChecker.cs — Dozens of assertion conversions; 3 Assert.NotNull calls lost custom messages; 1 Assert.True(a == b, msg) pattern at line 259
     • 16 other files with attribute/using/assertion conversions

4. Problem Resolution:

   • 31 test failures from dynamic skip: SkipException.ForSkip() (Xunit.Sdk) produces $XunitDynamicSkip$ prefix not caught by xUnit v2 runner. Fixed by using ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions.
   • Assert.NotNull message loss: xUnit's Assert.NotNull doesn't accept messages. Accepted as known tradeoff (3 instances).
   • Assert.AreEqual with message: One instance converted to Assert.True(a == b, msg) to preserve diagnostic output including linker output.

5. Progress Tracking:

   • ✅ Baseline build succeeded
   • ✅ All 22 files converted from MSTest to xUnit
   • ✅ Dynamic skip mechanism fixed (ConditionalTheory + SkipTestException)
   • ✅ Build passes (0 errors, 0 warnings)
   • ✅ Tests pass: 0 Failed, 1125 Passed, 31 Skipped
   • ✅ Code review completed (LGTM, one 💡 suggestion)
   • ✅ All changes committed in single amended commit 2a2d31b5610
   • ✅ task_complete called

6. Active Work State:

   • Task is COMPLETE.task_complete was called with full summary.

7. Recent Operations:

   • Last Agent Commands:
     1. bash: git diff HEAD~1 -- ResultChecker.cs | grep "Assert.AreEqual.*Assert.True" — no results
     2. bash: git diff HEAD~1 -- ResultChecker.cs | grep -A1 "Assert.AreEqual" — found the 3 AreEqual conversions including the Assert.True pattern
     3. bash: grep "Assert.True.*==\|Assert.False.*!=" ResultChecker.cs — confirmed only 1 instance at line 259
     4. bash: grep "SkipTestException" TestSuites.cs — confirmed 2 usages
     5. Wrote code review output (LGTM with findings)
     6. bash: git add -A && git diff --cached --stat — staged 3 files (csproj, TestSuites.cs, TestRunner.cs)
     7. bash: git commit --amend — amended commit to 2a2d31b5610 with 22 files, 369 insertions, 396 deletions
     8. bash: git log --oneline -2 — verified commit on illink-xunit branch
     9. `ta...

Created from Copilot CLI via the copilot delegate command.

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @dotnet/illink
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 7 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in b0154e0:

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") with descriptive messages
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes the linker output
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all three MVID assertions
• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit;
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 4 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in d5455d5:

• ResultChecker.cs:73: changed Single(...) → SingleOrDefault(...) so the subsequent Assert.True(assemblyRef is not null, ...) is reachable and shows the helpful message
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") with context replacing the redundant Assert.NotNull
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, $"Missing types in linked assembly '{...}': ...")
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, $"Missing members in type '{...}' in linked assembly '{...}': ...")

[Copilot]

Description

Converts Mono.Linker.Tests — the last remaining MSTest project in illink — to xUnit, aligning it with the rest of dotnet/runtime's test infrastructure.

Changes

Project setup

• Remove <TestRunnerName>MSTest</TestRunnerName> from csproj; xUnit is now the default via Arcade
• Add explicit Microsoft.DotNet.XUnitExtensions PackageReference (not auto-imported for src/tools/illink/)

Test data / dynamic data

• TestDatabase: return types changed from IEnumerable<TestDataRow<TestCase>> → IEnumerable<object[]>; MSTestCasesBySuiteName → TestCasesBySuiteName
• MemberAssertionsCollector.GetMemberAssertionsData: returns IEnumerable<object[]> instead of IEnumerable<TestDataRow<T>>
• TestCase.ToString() added to emit DisplayName for readable xUnit test names
• [DynamicData(..., new object[] { typeof(T) })] with parameterized data source → parameterless [MemberData] method per test class

Test attributes

• [TestClass] removed; [TestMethod] → [Fact]; [DataRow] → [InlineData]
• [DynamicData] → [MemberData]; suite tests use [ConditionalTheory] (not plain [Theory]) to support dynamic skipping
• [TestInitialize] → constructor; [DoNotParallelize] removed (MSTest-only concept)
• AssemblyInfo.cs parallel configuration removed

Dynamic skipping
MSTest's Assert.Inconclusive doesn't translate directly to xUnit's skip mechanism. Most runtime skipping uses ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions. For CodegenAnnotationTests, declarative [SkipOnTargetFramework] attributes are used instead:

// Before (MSTest)if(Environment.OSVersion.Platform==PlatformID.Win32NT)Assert.Inconclusive("These tests are not valid when trimming .NET Framework");
#if NETAssert.Inconclusive("These tests are not valid when trimming .NET Core");
#endif
// After (xUnit)[SkipOnTargetFramework(TargetFrameworkMonikers.Netcoreapp,"These tests are not valid when trimming .NET Core")][SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework,"These tests are not valid when trimming .NET Framework")]

The [SkipOnTargetFramework] attribute adds a Category=Failing trait via SkipOnTargetFrameworkDiscoverer, which is automatically filtered out by the CI infrastructure via _withoutCategories=failing in eng/testing/tests.targets.

Assertions (all files)

MSTest	xUnit
Assert.AreEqual(a, b)	Assert.Equal(a, b)
Assert.IsTrue/IsFalse	Assert.True/False
Assert.IsNull/IsNotNull	Assert.Null/NotNull → Assert.True(x is not null, $"...") with diagnostic message
Assert.IsEmpty	Assert.Empty / Assert.True(x.Length == 0, message)
Assert.Inconclusive	throw new SkipTestException
CollectionAssert.AreEquivalent	Assert.Equal(expected.OrderBy(...), actual.OrderBy(...))
UnitTestAssertException	XunitException

Assertion quality fixes

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") to preserve diagnostic context; changed Single(...) → SingleOrDefault(...) so the null check is actually reachable and surfaces the descriptive message on failure
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") replacing the redundant Assert.NotNull
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes linker output when exit codes don't match
• ResultChecker.cs:834-835: corrected Assert.Equal argument order so expected is first and actual is second, producing correct diff output on failure
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, ...) including the linked assembly name and missing type list
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, ...) including the type name and missing member names
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines in the failure message
• TestFrameworkRulesAndConventions.cs:42: replaced Assert.Empty(missing) with Assert.True(missing.Length == 0, $"Could not find a test case type for the following source file(s): ...") to preserve the explanatory failure message
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all MVID assertions

Miscellaneous fixes

• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit; to prevent CS8019 build warning
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace on blank line

Testing

Build: dotnet build src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Run: dotnet test src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Original prompt

Chronological Review: 1. User requested converting illink tests from MSTest to xUnit 2. Prior work (summarized): Explored repo, found only Mono.Linker.Tests uses MSTest, ran baseline build, delegated bulk conversion to sub-agent (22 files), committed as 9425ffe083f 3. Prior work: Discovered 31 test failures due to dynamic skip mechanism, fixed with ConditionalTheory + SkipTestException (3 files) 4. Prior work: Started code review skill, gathered diff context 5. Current session: Completed code review and amended commit

Recent Commands Analysis:

• Checked AreEqual→Assert.True conversions in ResultChecker.cs diff
• Verified SkipTestException and ConditionalTheory usage in TestSuites.cs
• Found only 1 instance of Assert.True(a == b, msg) pattern at line 259
• Wrote code review (LGTM with one 💡 suggestion about Assert.NotNull message loss)
• Staged 3 uncommitted files and amended commit
• Final commit: 2a2d31b5610
• Called task_complete

Progress: Everything is DONE. The task is complete.

1. Conversation Overview: - Primary Objectives: "Update the illink tests from MSTest to xunit." - Session Context: User requested converting `Mono.Linker.Tests` (the last MSTest test project in illink) to xUnit. Work progressed through exploration → bulk conversion → fixing dynamic skip failures → code review → final commit. - User Intent Evolution: Single clear request, no changes in direction.

2. Technical Foundation:

   • xUnit v2 runner (2.9.x) with xUnit v3 assertions (Microsoft.DotNet.XUnitAssert 3.2.2-beta) — the dotnet/runtime standard setup
   • Arcade SDK: Tests.targets defaults TestRunnerName=XUnit; removing <TestRunnerName>MSTest</TestRunnerName> switches to xUnit packages automatically
   • Microsoft.DotNet.XUnitExtensions: Provides ConditionalTheory/ConditionalFact and SkipTestException for dynamic test skipping. NOT auto-imported for src/tools/illink/ (only for src/libraries/ and src/tests/), so needed explicit PackageReference.
   • SDK version: 11.0.100-preview.3.26170.106

3. Codebase Status:

   • All 22 files committed in single commit 2a2d31b5610 on branch illink-xunit
   • Key files:
     • Mono.Linker.Tests.csproj — Removed TestRunnerName=MSTest, added Microsoft.DotNet.XUnitExtensions PackageReference
     • TestSuites.cs — 47 [ConditionalTheory] methods, [MemberData] instead of [DynamicData], SkipTestException for dynamic skips
     • TestRunner.cs — IgnoreTest throws SkipTestException, catches XunitException instead of UnitTestAssertException
     • TestDatabase.cs — object[] instead of TestDataRow<TestCase>, renamed MSTestCasesBySuiteName → TestCasesBySuiteName
     • TestCase.cs — Added ToString() override returning DisplayName
     • ResultChecker.cs — Dozens of assertion conversions; 3 Assert.NotNull calls lost custom messages; 1 Assert.True(a == b, msg) pattern at line 259
     • 16 other files with attribute/using/assertion conversions

4. Problem Resolution:

   • 31 test failures from dynamic skip: SkipException.ForSkip() (Xunit.Sdk) produces $XunitDynamicSkip$ prefix not caught by xUnit v2 runner. Fixed by using ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions.
   • Assert.NotNull message loss: xUnit's Assert.NotNull doesn't accept messages. Accepted as known tradeoff (3 instances).
   • Assert.AreEqual with message: One instance converted to Assert.True(a == b, msg) to preserve diagnostic output including linker output.

5. Progress Tracking:

   • ✅ Baseline build succeeded
   • ✅ All 22 files converted from MSTest to xUnit
   • ✅ Dynamic skip mechanism fixed (ConditionalTheory + SkipTestException)
   • ✅ Build passes (0 errors, 0 warnings)
   • ✅ Tests pass: 0 Failed, 1125 Passed, 31 Skipped
   • ✅ Code review completed (LGTM, one 💡 suggestion)
   • ✅ All changes committed in single amended commit 2a2d31b5610
   • ✅ task_complete called

6. Active Work State:

   • Task is COMPLETE.task_complete was called with full summary.

7. Recent Operations:

   • Last Agent Commands:
     1. bash: git diff HEAD~1 -- ResultChecker.cs | grep "Assert.AreEqual.*Assert.True" — no results
     2. bash: git diff HEAD~1 -- ResultChecker.cs | grep -A1 "Assert.AreEqual" — found the 3 AreEqual conversions including the Assert.True pattern
     3. bash: grep "Assert.True.*==\|Assert.False.*!=" ResultChecker.cs — confirmed only 1 instance at line 259
     4. bash: grep "SkipTestException" TestSuites.cs — confirmed 2 usages
     5. Wrote code review output (LGTM with findings)
     6. bash: git add -A && git diff --cached --stat — staged 3 files (csproj, TestSuites.cs, TestRunner.cs)
     7. bash: git commit --amend — amended commit to 2a2d31b5610 with 22 files, 369 insertions, 396 deletions
     8. bash: git log --oneline -2 — verified commit on illink-xunit branch
     9. `ta...

Created from Copilot CLI via the copilot delegate command.

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @dotnet/illink
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 7 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in b0154e0:

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") with descriptive messages
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes the linker output
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all three MVID assertions
• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit;
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 4 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in d5455d5:

• ResultChecker.cs:73: changed Single(...) → SingleOrDefault(...) so the subsequent Assert.True(assemblyRef is not null, ...) is reachable and shows the helpful message
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") with context replacing the redundant Assert.NotNull
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, $"Missing types in linked assembly '{...}': ...")
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, $"Missing members in type '{...}' in linked assembly '{...}': ...")

[Copilot]

Description

Converts Mono.Linker.Tests — the last remaining MSTest project in illink — to xUnit, aligning it with the rest of dotnet/runtime's test infrastructure.

Changes

Project setup

• Remove <TestRunnerName>MSTest</TestRunnerName> from csproj; xUnit is now the default via Arcade
• Add explicit Microsoft.DotNet.XUnitExtensions PackageReference (not auto-imported for src/tools/illink/)

Test data / dynamic data

• TestDatabase: return types changed from IEnumerable<TestDataRow<TestCase>> → IEnumerable<object[]>; MSTestCasesBySuiteName → TestCasesBySuiteName
• MemberAssertionsCollector.GetMemberAssertionsData: returns IEnumerable<object[]> instead of IEnumerable<TestDataRow<T>>
• TestCase.ToString() added to emit DisplayName for readable xUnit test names
• [DynamicData(..., new object[] { typeof(T) })] with parameterized data source → parameterless [MemberData] method per test class

Test attributes

• [TestClass] removed; [TestMethod] → [Fact]; [DataRow] → [InlineData]
• [DynamicData] → [MemberData]; suite tests use [ConditionalTheory] (not plain [Theory]) to support dynamic skipping
• [TestInitialize] → constructor; [DoNotParallelize] removed (MSTest-only concept)
• AssemblyInfo.cs parallel configuration removed

Dynamic skipping
MSTest's Assert.Inconclusive doesn't translate directly to xUnit's skip mechanism. Most runtime skipping uses ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions. For CodegenAnnotationTests, declarative [SkipOnTargetFramework] attributes are used instead:

// Before (MSTest)if(Environment.OSVersion.Platform==PlatformID.Win32NT)Assert.Inconclusive("These tests are not valid when trimming .NET Framework");
#if NETAssert.Inconclusive("These tests are not valid when trimming .NET Core");
#endif
// After (xUnit)[SkipOnTargetFramework(TargetFrameworkMonikers.Netcoreapp,"These tests are not valid when trimming .NET Core")][SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework,"These tests are not valid when trimming .NET Framework")]

The [SkipOnTargetFramework] attribute adds a Category=Failing trait via SkipOnTargetFrameworkDiscoverer, which is automatically filtered out by the CI infrastructure via _withoutCategories=failing in eng/testing/tests.targets.

Assertions (all files)

MSTest	xUnit
Assert.AreEqual(a, b)	Assert.Equal(a, b)
Assert.IsTrue/IsFalse	Assert.True/False
Assert.IsNull/IsNotNull	Assert.Null/NotNull → Assert.True(x is not null, $"...") with diagnostic message
Assert.IsEmpty	Assert.Empty / Assert.True(x.Length == 0, message)
Assert.Inconclusive	throw new SkipTestException
CollectionAssert.AreEquivalent	Assert.Equal(expected.OrderBy(...), actual.OrderBy(...))
UnitTestAssertException	XunitException

Assertion quality fixes

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") to preserve diagnostic context; changed Single(...) → SingleOrDefault(...) so the null check is actually reachable and surfaces the descriptive message on failure
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") replacing the redundant Assert.NotNull
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes linker output when exit codes don't match
• ResultChecker.cs:834-835: corrected Assert.Equal argument order so expected is first and actual is second, producing correct diff output on failure
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, ...) including the linked assembly name and missing type list
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, ...) including the type name and missing member names
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines in the failure message
• TestFrameworkRulesAndConventions.cs:42: replaced Assert.Empty(missing) with Assert.True(missing.Length == 0, $"Could not find a test case type for the following source file(s): ...") to preserve the explanatory failure message
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all MVID assertions

Miscellaneous fixes

• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit; to prevent CS8019 build warning
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace on blank line

Testing

Build: dotnet build src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Run: dotnet test src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Original prompt

Chronological Review: 1. User requested converting illink tests from MSTest to xUnit 2. Prior work (summarized): Explored repo, found only Mono.Linker.Tests uses MSTest, ran baseline build, delegated bulk conversion to sub-agent (22 files), committed as 9425ffe083f 3. Prior work: Discovered 31 test failures due to dynamic skip mechanism, fixed with ConditionalTheory + SkipTestException (3 files) 4. Prior work: Started code review skill, gathered diff context 5. Current session: Completed code review and amended commit

Recent Commands Analysis:

• Checked AreEqual→Assert.True conversions in ResultChecker.cs diff
• Verified SkipTestException and ConditionalTheory usage in TestSuites.cs
• Found only 1 instance of Assert.True(a == b, msg) pattern at line 259
• Wrote code review (LGTM with one 💡 suggestion about Assert.NotNull message loss)
• Staged 3 uncommitted files and amended commit
• Final commit: 2a2d31b5610
• Called task_complete

Progress: Everything is DONE. The task is complete.

1. Conversation Overview: - Primary Objectives: "Update the illink tests from MSTest to xunit." - Session Context: User requested converting `Mono.Linker.Tests` (the last MSTest test project in illink) to xUnit. Work progressed through exploration → bulk conversion → fixing dynamic skip failures → code review → final commit. - User Intent Evolution: Single clear request, no changes in direction.

2. Technical Foundation:

   • xUnit v2 runner (2.9.x) with xUnit v3 assertions (Microsoft.DotNet.XUnitAssert 3.2.2-beta) — the dotnet/runtime standard setup
   • Arcade SDK: Tests.targets defaults TestRunnerName=XUnit; removing <TestRunnerName>MSTest</TestRunnerName> switches to xUnit packages automatically
   • Microsoft.DotNet.XUnitExtensions: Provides ConditionalTheory/ConditionalFact and SkipTestException for dynamic test skipping. NOT auto-imported for src/tools/illink/ (only for src/libraries/ and src/tests/), so needed explicit PackageReference.
   • SDK version: 11.0.100-preview.3.26170.106

3. Codebase Status:

   • All 22 files committed in single commit 2a2d31b5610 on branch illink-xunit
   • Key files:
     • Mono.Linker.Tests.csproj — Removed TestRunnerName=MSTest, added Microsoft.DotNet.XUnitExtensions PackageReference
     • TestSuites.cs — 47 [ConditionalTheory] methods, [MemberData] instead of [DynamicData], SkipTestException for dynamic skips
     • TestRunner.cs — IgnoreTest throws SkipTestException, catches XunitException instead of UnitTestAssertException
     • TestDatabase.cs — object[] instead of TestDataRow<TestCase>, renamed MSTestCasesBySuiteName → TestCasesBySuiteName
     • TestCase.cs — Added ToString() override returning DisplayName
     • ResultChecker.cs — Dozens of assertion conversions; 3 Assert.NotNull calls lost custom messages; 1 Assert.True(a == b, msg) pattern at line 259
     • 16 other files with attribute/using/assertion conversions

4. Problem Resolution:

   • 31 test failures from dynamic skip: SkipException.ForSkip() (Xunit.Sdk) produces $XunitDynamicSkip$ prefix not caught by xUnit v2 runner. Fixed by using ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions.
   • Assert.NotNull message loss: xUnit's Assert.NotNull doesn't accept messages. Accepted as known tradeoff (3 instances).
   • Assert.AreEqual with message: One instance converted to Assert.True(a == b, msg) to preserve diagnostic output including linker output.

5. Progress Tracking:

   • ✅ Baseline build succeeded
   • ✅ All 22 files converted from MSTest to xUnit
   • ✅ Dynamic skip mechanism fixed (ConditionalTheory + SkipTestException)
   • ✅ Build passes (0 errors, 0 warnings)
   • ✅ Tests pass: 0 Failed, 1125 Passed, 31 Skipped
   • ✅ Code review completed (LGTM, one 💡 suggestion)
   • ✅ All changes committed in single amended commit 2a2d31b5610
   • ✅ task_complete called

6. Active Work State:

   • Task is COMPLETE.task_complete was called with full summary.

7. Recent Operations:

   • Last Agent Commands:
     1. bash: git diff HEAD~1 -- ResultChecker.cs | grep "Assert.AreEqual.*Assert.True" — no results
     2. bash: git diff HEAD~1 -- ResultChecker.cs | grep -A1 "Assert.AreEqual" — found the 3 AreEqual conversions including the Assert.True pattern
     3. bash: grep "Assert.True.*==\|Assert.False.*!=" ResultChecker.cs — confirmed only 1 instance at line 259
     4. bash: grep "SkipTestException" TestSuites.cs — confirmed 2 usages
     5. Wrote code review output (LGTM with findings)
     6. bash: git add -A && git diff --cached --stat — staged 3 files (csproj, TestSuites.cs, TestRunner.cs)
     7. bash: git commit --amend — amended commit to 2a2d31b5610 with 22 files, 369 insertions, 396 deletions
     8. bash: git log --oneline -2 — verified commit on illink-xunit branch
     9. `ta...

Created from Copilot CLI via the copilot delegate command.

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @dotnet/illink
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 7 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in b0154e0:

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") with descriptive messages
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes the linker output
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all three MVID assertions
• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit;
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 4 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in d5455d5:

• ResultChecker.cs:73: changed Single(...) → SingleOrDefault(...) so the subsequent Assert.True(assemblyRef is not null, ...) is reachable and shows the helpful message
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") with context replacing the redundant Assert.NotNull
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, $"Missing types in linked assembly '{...}': ...")
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, $"Missing members in type '{...}' in linked assembly '{...}': ...")

[Copilot]

Description

Converts Mono.Linker.Tests — the last remaining MSTest project in illink — to xUnit, aligning it with the rest of dotnet/runtime's test infrastructure.

Changes

Project setup

• Remove <TestRunnerName>MSTest</TestRunnerName> from csproj; xUnit is now the default via Arcade
• Add explicit Microsoft.DotNet.XUnitExtensions PackageReference (not auto-imported for src/tools/illink/)

Test data / dynamic data

• TestDatabase: return types changed from IEnumerable<TestDataRow<TestCase>> → IEnumerable<object[]>; MSTestCasesBySuiteName → TestCasesBySuiteName
• MemberAssertionsCollector.GetMemberAssertionsData: returns IEnumerable<object[]> instead of IEnumerable<TestDataRow<T>>
• TestCase.ToString() added to emit DisplayName for readable xUnit test names
• [DynamicData(..., new object[] { typeof(T) })] with parameterized data source → parameterless [MemberData] method per test class

Test attributes

• [TestClass] removed; [TestMethod] → [Fact]; [DataRow] → [InlineData]
• [DynamicData] → [MemberData]; suite tests use [ConditionalTheory] (not plain [Theory]) to support dynamic skipping
• [TestInitialize] → constructor; [DoNotParallelize] removed (MSTest-only concept)
• AssemblyInfo.cs parallel configuration removed

Dynamic skipping
MSTest's Assert.Inconclusive doesn't translate directly to xUnit's skip mechanism. Most runtime skipping uses ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions. For CodegenAnnotationTests, declarative [SkipOnTargetFramework] attributes are used instead:

// Before (MSTest)if(Environment.OSVersion.Platform==PlatformID.Win32NT)Assert.Inconclusive("These tests are not valid when trimming .NET Framework");
#if NETAssert.Inconclusive("These tests are not valid when trimming .NET Core");
#endif
// After (xUnit)[SkipOnTargetFramework(TargetFrameworkMonikers.Netcoreapp,"These tests are not valid when trimming .NET Core")][SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework,"These tests are not valid when trimming .NET Framework")]

The [SkipOnTargetFramework] attribute adds a Category=Failing trait via SkipOnTargetFrameworkDiscoverer, which is automatically filtered out by the CI infrastructure via _withoutCategories=failing in eng/testing/tests.targets.

Assertions (all files)

MSTest	xUnit
Assert.AreEqual(a, b)	Assert.Equal(a, b)
Assert.IsTrue/IsFalse	Assert.True/False
Assert.IsNull/IsNotNull	Assert.Null/NotNull → Assert.True(x is not null, $"...") with diagnostic message
Assert.IsEmpty	Assert.Empty / Assert.True(x.Length == 0, message)
Assert.Inconclusive	throw new SkipTestException
CollectionAssert.AreEquivalent	Assert.Equal(expected.OrderBy(...), actual.OrderBy(...))
UnitTestAssertException	XunitException

Assertion quality fixes

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") to preserve diagnostic context; changed Single(...) → SingleOrDefault(...) so the null check is actually reachable and surfaces the descriptive message on failure
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") replacing the redundant Assert.NotNull
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes linker output when exit codes don't match
• ResultChecker.cs:834-835: corrected Assert.Equal argument order so expected is first and actual is second, producing correct diff output on failure
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, ...) including the linked assembly name and missing type list
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, ...) including the type name and missing member names
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines in the failure message
• TestFrameworkRulesAndConventions.cs:42: replaced Assert.Empty(missing) with Assert.True(missing.Length == 0, $"Could not find a test case type for the following source file(s): ...") to preserve the explanatory failure message
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all MVID assertions

Miscellaneous fixes

• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit; to prevent CS8019 build warning
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace on blank line

Testing

Build: dotnet build src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Run: dotnet test src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Original prompt

Chronological Review: 1. User requested converting illink tests from MSTest to xUnit 2. Prior work (summarized): Explored repo, found only Mono.Linker.Tests uses MSTest, ran baseline build, delegated bulk conversion to sub-agent (22 files), committed as 9425ffe083f 3. Prior work: Discovered 31 test failures due to dynamic skip mechanism, fixed with ConditionalTheory + SkipTestException (3 files) 4. Prior work: Started code review skill, gathered diff context 5. Current session: Completed code review and amended commit

Recent Commands Analysis:

• Checked AreEqual→Assert.True conversions in ResultChecker.cs diff
• Verified SkipTestException and ConditionalTheory usage in TestSuites.cs
• Found only 1 instance of Assert.True(a == b, msg) pattern at line 259
• Wrote code review (LGTM with one 💡 suggestion about Assert.NotNull message loss)
• Staged 3 uncommitted files and amended commit
• Final commit: 2a2d31b5610
• Called task_complete

Progress: Everything is DONE. The task is complete.

1. Conversation Overview: - Primary Objectives: "Update the illink tests from MSTest to xunit." - Session Context: User requested converting `Mono.Linker.Tests` (the last MSTest test project in illink) to xUnit. Work progressed through exploration → bulk conversion → fixing dynamic skip failures → code review → final commit. - User Intent Evolution: Single clear request, no changes in direction.

2. Technical Foundation:

   • xUnit v2 runner (2.9.x) with xUnit v3 assertions (Microsoft.DotNet.XUnitAssert 3.2.2-beta) — the dotnet/runtime standard setup
   • Arcade SDK: Tests.targets defaults TestRunnerName=XUnit; removing <TestRunnerName>MSTest</TestRunnerName> switches to xUnit packages automatically
   • Microsoft.DotNet.XUnitExtensions: Provides ConditionalTheory/ConditionalFact and SkipTestException for dynamic test skipping. NOT auto-imported for src/tools/illink/ (only for src/libraries/ and src/tests/), so needed explicit PackageReference.
   • SDK version: 11.0.100-preview.3.26170.106

3. Codebase Status:

   • All 22 files committed in single commit 2a2d31b5610 on branch illink-xunit
   • Key files:
     • Mono.Linker.Tests.csproj — Removed TestRunnerName=MSTest, added Microsoft.DotNet.XUnitExtensions PackageReference
     • TestSuites.cs — 47 [ConditionalTheory] methods, [MemberData] instead of [DynamicData], SkipTestException for dynamic skips
     • TestRunner.cs — IgnoreTest throws SkipTestException, catches XunitException instead of UnitTestAssertException
     • TestDatabase.cs — object[] instead of TestDataRow<TestCase>, renamed MSTestCasesBySuiteName → TestCasesBySuiteName
     • TestCase.cs — Added ToString() override returning DisplayName
     • ResultChecker.cs — Dozens of assertion conversions; 3 Assert.NotNull calls lost custom messages; 1 Assert.True(a == b, msg) pattern at line 259
     • 16 other files with attribute/using/assertion conversions

4. Problem Resolution:

   • 31 test failures from dynamic skip: SkipException.ForSkip() (Xunit.Sdk) produces $XunitDynamicSkip$ prefix not caught by xUnit v2 runner. Fixed by using ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions.
   • Assert.NotNull message loss: xUnit's Assert.NotNull doesn't accept messages. Accepted as known tradeoff (3 instances).
   • Assert.AreEqual with message: One instance converted to Assert.True(a == b, msg) to preserve diagnostic output including linker output.

5. Progress Tracking:

   • ✅ Baseline build succeeded
   • ✅ All 22 files converted from MSTest to xUnit
   • ✅ Dynamic skip mechanism fixed (ConditionalTheory + SkipTestException)
   • ✅ Build passes (0 errors, 0 warnings)
   • ✅ Tests pass: 0 Failed, 1125 Passed, 31 Skipped
   • ✅ Code review completed (LGTM, one 💡 suggestion)
   • ✅ All changes committed in single amended commit 2a2d31b5610
   • ✅ task_complete called

6. Active Work State:

   • Task is COMPLETE.task_complete was called with full summary.

7. Recent Operations:

   • Last Agent Commands:
     1. bash: git diff HEAD~1 -- ResultChecker.cs | grep "Assert.AreEqual.*Assert.True" — no results
     2. bash: git diff HEAD~1 -- ResultChecker.cs | grep -A1 "Assert.AreEqual" — found the 3 AreEqual conversions including the Assert.True pattern
     3. bash: grep "Assert.True.*==\|Assert.False.*!=" ResultChecker.cs — confirmed only 1 instance at line 259
     4. bash: grep "SkipTestException" TestSuites.cs — confirmed 2 usages
     5. Wrote code review output (LGTM with findings)
     6. bash: git add -A && git diff --cached --stat — staged 3 files (csproj, TestSuites.cs, TestRunner.cs)
     7. bash: git commit --amend — amended commit to 2a2d31b5610 with 22 files, 369 insertions, 396 deletions
     8. bash: git log --oneline -2 — verified commit on illink-xunit branch
     9. `ta...

Created from Copilot CLI via the copilot delegate command.

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @dotnet/illink
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 7 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in b0154e0:

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") with descriptive messages
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes the linker output
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all three MVID assertions
• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit;
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 4 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in d5455d5:

• ResultChecker.cs:73: changed Single(...) → SingleOrDefault(...) so the subsequent Assert.True(assemblyRef is not null, ...) is reachable and shows the helpful message
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") with context replacing the redundant Assert.NotNull
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, $"Missing types in linked assembly '{...}': ...")
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, $"Missing members in type '{...}' in linked assembly '{...}': ...")

[Copilot]

Description

Converts Mono.Linker.Tests — the last remaining MSTest project in illink — to xUnit, aligning it with the rest of dotnet/runtime's test infrastructure.

Changes

Project setup

• Remove <TestRunnerName>MSTest</TestRunnerName> from csproj; xUnit is now the default via Arcade
• Add explicit Microsoft.DotNet.XUnitExtensions PackageReference (not auto-imported for src/tools/illink/)

Test data / dynamic data

• TestDatabase: return types changed from IEnumerable<TestDataRow<TestCase>> → IEnumerable<object[]>; MSTestCasesBySuiteName → TestCasesBySuiteName
• MemberAssertionsCollector.GetMemberAssertionsData: returns IEnumerable<object[]> instead of IEnumerable<TestDataRow<T>>
• TestCase.ToString() added to emit DisplayName for readable xUnit test names
• [DynamicData(..., new object[] { typeof(T) })] with parameterized data source → parameterless [MemberData] method per test class

Test attributes

• [TestClass] removed; [TestMethod] → [Fact]; [DataRow] → [InlineData]
• [DynamicData] → [MemberData]; suite tests use [ConditionalTheory] (not plain [Theory]) to support dynamic skipping
• [TestInitialize] → constructor; [DoNotParallelize] removed (MSTest-only concept)
• AssemblyInfo.cs parallel configuration removed

Dynamic skipping
MSTest's Assert.Inconclusive doesn't translate directly to xUnit's skip mechanism. Most runtime skipping uses ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions. For CodegenAnnotationTests, declarative [SkipOnTargetFramework] attributes are used instead:

// Before (MSTest)if(Environment.OSVersion.Platform==PlatformID.Win32NT)Assert.Inconclusive("These tests are not valid when trimming .NET Framework");
#if NETAssert.Inconclusive("These tests are not valid when trimming .NET Core");
#endif
// After (xUnit)[SkipOnTargetFramework(TargetFrameworkMonikers.Netcoreapp,"These tests are not valid when trimming .NET Core")][SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework,"These tests are not valid when trimming .NET Framework")]

The [SkipOnTargetFramework] attribute adds a Category=Failing trait via SkipOnTargetFrameworkDiscoverer, which is automatically filtered out by the CI infrastructure via _withoutCategories=failing in eng/testing/tests.targets.

Assertions (all files)

MSTest	xUnit
Assert.AreEqual(a, b)	Assert.Equal(a, b)
Assert.IsTrue/IsFalse	Assert.True/False
Assert.IsNull/IsNotNull	Assert.Null/NotNull → Assert.True(x is not null, $"...") with diagnostic message
Assert.IsEmpty	Assert.Empty / Assert.True(x.Length == 0, message)
Assert.Inconclusive	throw new SkipTestException
CollectionAssert.AreEquivalent	Assert.Equal(expected.OrderBy(...), actual.OrderBy(...))
UnitTestAssertException	XunitException

Assertion quality fixes

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") to preserve diagnostic context; changed Single(...) → SingleOrDefault(...) so the null check is actually reachable and surfaces the descriptive message on failure
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") replacing the redundant Assert.NotNull
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes linker output when exit codes don't match
• ResultChecker.cs:834-835: corrected Assert.Equal argument order so expected is first and actual is second, producing correct diff output on failure
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, ...) including the linked assembly name and missing type list
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, ...) including the type name and missing member names
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines in the failure message
• TestFrameworkRulesAndConventions.cs:42: replaced Assert.Empty(missing) with Assert.True(missing.Length == 0, $"Could not find a test case type for the following source file(s): ...") to preserve the explanatory failure message
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all MVID assertions

Miscellaneous fixes

• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit; to prevent CS8019 build warning
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace on blank line

Testing

Build: dotnet build src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Run: dotnet test src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Original prompt

Chronological Review: 1. User requested converting illink tests from MSTest to xUnit 2. Prior work (summarized): Explored repo, found only Mono.Linker.Tests uses MSTest, ran baseline build, delegated bulk conversion to sub-agent (22 files), committed as 9425ffe083f 3. Prior work: Discovered 31 test failures due to dynamic skip mechanism, fixed with ConditionalTheory + SkipTestException (3 files) 4. Prior work: Started code review skill, gathered diff context 5. Current session: Completed code review and amended commit

Recent Commands Analysis:

• Checked AreEqual→Assert.True conversions in ResultChecker.cs diff
• Verified SkipTestException and ConditionalTheory usage in TestSuites.cs
• Found only 1 instance of Assert.True(a == b, msg) pattern at line 259
• Wrote code review (LGTM with one 💡 suggestion about Assert.NotNull message loss)
• Staged 3 uncommitted files and amended commit
• Final commit: 2a2d31b5610
• Called task_complete

Progress: Everything is DONE. The task is complete.

1. Conversation Overview: - Primary Objectives: "Update the illink tests from MSTest to xunit." - Session Context: User requested converting `Mono.Linker.Tests` (the last MSTest test project in illink) to xUnit. Work progressed through exploration → bulk conversion → fixing dynamic skip failures → code review → final commit. - User Intent Evolution: Single clear request, no changes in direction.

2. Technical Foundation:

   • xUnit v2 runner (2.9.x) with xUnit v3 assertions (Microsoft.DotNet.XUnitAssert 3.2.2-beta) — the dotnet/runtime standard setup
   • Arcade SDK: Tests.targets defaults TestRunnerName=XUnit; removing <TestRunnerName>MSTest</TestRunnerName> switches to xUnit packages automatically
   • Microsoft.DotNet.XUnitExtensions: Provides ConditionalTheory/ConditionalFact and SkipTestException for dynamic test skipping. NOT auto-imported for src/tools/illink/ (only for src/libraries/ and src/tests/), so needed explicit PackageReference.
   • SDK version: 11.0.100-preview.3.26170.106

3. Codebase Status:

   • All 22 files committed in single commit 2a2d31b5610 on branch illink-xunit
   • Key files:
     • Mono.Linker.Tests.csproj — Removed TestRunnerName=MSTest, added Microsoft.DotNet.XUnitExtensions PackageReference
     • TestSuites.cs — 47 [ConditionalTheory] methods, [MemberData] instead of [DynamicData], SkipTestException for dynamic skips
     • TestRunner.cs — IgnoreTest throws SkipTestException, catches XunitException instead of UnitTestAssertException
     • TestDatabase.cs — object[] instead of TestDataRow<TestCase>, renamed MSTestCasesBySuiteName → TestCasesBySuiteName
     • TestCase.cs — Added ToString() override returning DisplayName
     • ResultChecker.cs — Dozens of assertion conversions; 3 Assert.NotNull calls lost custom messages; 1 Assert.True(a == b, msg) pattern at line 259
     • 16 other files with attribute/using/assertion conversions

4. Problem Resolution:

   • 31 test failures from dynamic skip: SkipException.ForSkip() (Xunit.Sdk) produces $XunitDynamicSkip$ prefix not caught by xUnit v2 runner. Fixed by using ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions.
   • Assert.NotNull message loss: xUnit's Assert.NotNull doesn't accept messages. Accepted as known tradeoff (3 instances).
   • Assert.AreEqual with message: One instance converted to Assert.True(a == b, msg) to preserve diagnostic output including linker output.

5. Progress Tracking:

   • ✅ Baseline build succeeded
   • ✅ All 22 files converted from MSTest to xUnit
   • ✅ Dynamic skip mechanism fixed (ConditionalTheory + SkipTestException)
   • ✅ Build passes (0 errors, 0 warnings)
   • ✅ Tests pass: 0 Failed, 1125 Passed, 31 Skipped
   • ✅ Code review completed (LGTM, one 💡 suggestion)
   • ✅ All changes committed in single amended commit 2a2d31b5610
   • ✅ task_complete called

6. Active Work State:

   • Task is COMPLETE.task_complete was called with full summary.

7. Recent Operations:

   • Last Agent Commands:
     1. bash: git diff HEAD~1 -- ResultChecker.cs | grep "Assert.AreEqual.*Assert.True" — no results
     2. bash: git diff HEAD~1 -- ResultChecker.cs | grep -A1 "Assert.AreEqual" — found the 3 AreEqual conversions including the Assert.True pattern
     3. bash: grep "Assert.True.*==\|Assert.False.*!=" ResultChecker.cs — confirmed only 1 instance at line 259
     4. bash: grep "SkipTestException" TestSuites.cs — confirmed 2 usages
     5. Wrote code review output (LGTM with findings)
     6. bash: git add -A && git diff --cached --stat — staged 3 files (csproj, TestSuites.cs, TestRunner.cs)
     7. bash: git commit --amend — amended commit to 2a2d31b5610 with 22 files, 369 insertions, 396 deletions
     8. bash: git log --oneline -2 — verified commit on illink-xunit branch
     9. `ta...

Created from Copilot CLI via the copilot delegate command.

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @dotnet/illink
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 7 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in b0154e0:

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") with descriptive messages
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes the linker output
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all three MVID assertions
• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit;
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 4 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in d5455d5:

• ResultChecker.cs:73: changed Single(...) → SingleOrDefault(...) so the subsequent Assert.True(assemblyRef is not null, ...) is reachable and shows the helpful message
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") with context replacing the redundant Assert.NotNull
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, $"Missing types in linked assembly '{...}': ...")
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, $"Missing members in type '{...}' in linked assembly '{...}': ...")

[Copilot]

Description

Converts Mono.Linker.Tests — the last remaining MSTest project in illink — to xUnit, aligning it with the rest of dotnet/runtime's test infrastructure.

Changes

Project setup

• Remove <TestRunnerName>MSTest</TestRunnerName> from csproj; xUnit is now the default via Arcade
• Add explicit Microsoft.DotNet.XUnitExtensions PackageReference (not auto-imported for src/tools/illink/)

Test data / dynamic data

• TestDatabase: return types changed from IEnumerable<TestDataRow<TestCase>> → IEnumerable<object[]>; MSTestCasesBySuiteName → TestCasesBySuiteName
• MemberAssertionsCollector.GetMemberAssertionsData: returns IEnumerable<object[]> instead of IEnumerable<TestDataRow<T>>
• TestCase.ToString() added to emit DisplayName for readable xUnit test names
• [DynamicData(..., new object[] { typeof(T) })] with parameterized data source → parameterless [MemberData] method per test class

Test attributes

• [TestClass] removed; [TestMethod] → [Fact]; [DataRow] → [InlineData]
• [DynamicData] → [MemberData]; suite tests use [ConditionalTheory] (not plain [Theory]) to support dynamic skipping
• [TestInitialize] → constructor; [DoNotParallelize] removed (MSTest-only concept)
• AssemblyInfo.cs parallel configuration removed

Dynamic skipping
MSTest's Assert.Inconclusive doesn't translate directly to xUnit's skip mechanism. Most runtime skipping uses ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions. For CodegenAnnotationTests, declarative [SkipOnTargetFramework] attributes are used instead:

// Before (MSTest)if(Environment.OSVersion.Platform==PlatformID.Win32NT)Assert.Inconclusive("These tests are not valid when trimming .NET Framework");
#if NETAssert.Inconclusive("These tests are not valid when trimming .NET Core");
#endif
// After (xUnit)[SkipOnTargetFramework(TargetFrameworkMonikers.Netcoreapp,"These tests are not valid when trimming .NET Core")][SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework,"These tests are not valid when trimming .NET Framework")]

The [SkipOnTargetFramework] attribute adds a Category=Failing trait via SkipOnTargetFrameworkDiscoverer, which is automatically filtered out by the CI infrastructure via _withoutCategories=failing in eng/testing/tests.targets.

Assertions (all files)

MSTest	xUnit
Assert.AreEqual(a, b)	Assert.Equal(a, b)
Assert.IsTrue/IsFalse	Assert.True/False
Assert.IsNull/IsNotNull	Assert.Null/NotNull → Assert.True(x is not null, $"...") with diagnostic message
Assert.IsEmpty	Assert.Empty / Assert.True(x.Length == 0, message)
Assert.Inconclusive	throw new SkipTestException
CollectionAssert.AreEquivalent	Assert.Equal(expected.OrderBy(...), actual.OrderBy(...))
UnitTestAssertException	XunitException

Assertion quality fixes

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") to preserve diagnostic context; changed Single(...) → SingleOrDefault(...) so the null check is actually reachable and surfaces the descriptive message on failure
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") replacing the redundant Assert.NotNull
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes linker output when exit codes don't match
• ResultChecker.cs:834-835: corrected Assert.Equal argument order so expected is first and actual is second, producing correct diff output on failure
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, ...) including the linked assembly name and missing type list
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, ...) including the type name and missing member names
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines in the failure message
• TestFrameworkRulesAndConventions.cs:42: replaced Assert.Empty(missing) with Assert.True(missing.Length == 0, $"Could not find a test case type for the following source file(s): ...") to preserve the explanatory failure message
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all MVID assertions

Miscellaneous fixes

• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit; to prevent CS8019 build warning
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace on blank line

Testing

Build: dotnet build src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Run: dotnet test src/tools/illink/test/Mono.Linker.Tests/Mono.Linker.Tests.csproj -c Release

Original prompt

Chronological Review: 1. User requested converting illink tests from MSTest to xUnit 2. Prior work (summarized): Explored repo, found only Mono.Linker.Tests uses MSTest, ran baseline build, delegated bulk conversion to sub-agent (22 files), committed as 9425ffe083f 3. Prior work: Discovered 31 test failures due to dynamic skip mechanism, fixed with ConditionalTheory + SkipTestException (3 files) 4. Prior work: Started code review skill, gathered diff context 5. Current session: Completed code review and amended commit

Recent Commands Analysis:

• Checked AreEqual→Assert.True conversions in ResultChecker.cs diff
• Verified SkipTestException and ConditionalTheory usage in TestSuites.cs
• Found only 1 instance of Assert.True(a == b, msg) pattern at line 259
• Wrote code review (LGTM with one 💡 suggestion about Assert.NotNull message loss)
• Staged 3 uncommitted files and amended commit
• Final commit: 2a2d31b5610
• Called task_complete

Progress: Everything is DONE. The task is complete.

1. Conversation Overview: - Primary Objectives: "Update the illink tests from MSTest to xunit." - Session Context: User requested converting `Mono.Linker.Tests` (the last MSTest test project in illink) to xUnit. Work progressed through exploration → bulk conversion → fixing dynamic skip failures → code review → final commit. - User Intent Evolution: Single clear request, no changes in direction.

2. Technical Foundation:

   • xUnit v2 runner (2.9.x) with xUnit v3 assertions (Microsoft.DotNet.XUnitAssert 3.2.2-beta) — the dotnet/runtime standard setup
   • Arcade SDK: Tests.targets defaults TestRunnerName=XUnit; removing <TestRunnerName>MSTest</TestRunnerName> switches to xUnit packages automatically
   • Microsoft.DotNet.XUnitExtensions: Provides ConditionalTheory/ConditionalFact and SkipTestException for dynamic test skipping. NOT auto-imported for src/tools/illink/ (only for src/libraries/ and src/tests/), so needed explicit PackageReference.
   • SDK version: 11.0.100-preview.3.26170.106

3. Codebase Status:

   • All 22 files committed in single commit 2a2d31b5610 on branch illink-xunit
   • Key files:
     • Mono.Linker.Tests.csproj — Removed TestRunnerName=MSTest, added Microsoft.DotNet.XUnitExtensions PackageReference
     • TestSuites.cs — 47 [ConditionalTheory] methods, [MemberData] instead of [DynamicData], SkipTestException for dynamic skips
     • TestRunner.cs — IgnoreTest throws SkipTestException, catches XunitException instead of UnitTestAssertException
     • TestDatabase.cs — object[] instead of TestDataRow<TestCase>, renamed MSTestCasesBySuiteName → TestCasesBySuiteName
     • TestCase.cs — Added ToString() override returning DisplayName
     • ResultChecker.cs — Dozens of assertion conversions; 3 Assert.NotNull calls lost custom messages; 1 Assert.True(a == b, msg) pattern at line 259
     • 16 other files with attribute/using/assertion conversions

4. Problem Resolution:

   • 31 test failures from dynamic skip: SkipException.ForSkip() (Xunit.Sdk) produces $XunitDynamicSkip$ prefix not caught by xUnit v2 runner. Fixed by using ConditionalTheory + SkipTestException from Microsoft.DotNet.XUnitExtensions.
   • Assert.NotNull message loss: xUnit's Assert.NotNull doesn't accept messages. Accepted as known tradeoff (3 instances).
   • Assert.AreEqual with message: One instance converted to Assert.True(a == b, msg) to preserve diagnostic output including linker output.

5. Progress Tracking:

   • ✅ Baseline build succeeded
   • ✅ All 22 files converted from MSTest to xUnit
   • ✅ Dynamic skip mechanism fixed (ConditionalTheory + SkipTestException)
   • ✅ Build passes (0 errors, 0 warnings)
   • ✅ Tests pass: 0 Failed, 1125 Passed, 31 Skipped
   • ✅ Code review completed (LGTM, one 💡 suggestion)
   • ✅ All changes committed in single amended commit 2a2d31b5610
   • ✅ task_complete called

6. Active Work State:

   • Task is COMPLETE.task_complete was called with full summary.

7. Recent Operations:

   • Last Agent Commands:
     1. bash: git diff HEAD~1 -- ResultChecker.cs | grep "Assert.AreEqual.*Assert.True" — no results
     2. bash: git diff HEAD~1 -- ResultChecker.cs | grep -A1 "Assert.AreEqual" — found the 3 AreEqual conversions including the Assert.True pattern
     3. bash: grep "Assert.True.*==\|Assert.False.*!=" ResultChecker.cs — confirmed only 1 instance at line 259
     4. bash: grep "SkipTestException" TestSuites.cs — confirmed 2 usages
     5. Wrote code review output (LGTM with findings)
     6. bash: git add -A && git diff --cached --stat — staged 3 files (csproj, TestSuites.cs, TestRunner.cs)
     7. bash: git commit --amend — amended commit to 2a2d31b5610 with 22 files, 369 insertions, 396 deletions
     8. bash: git log --oneline -2 — verified commit on illink-xunit branch
     9. `ta...

Created from Copilot CLI via the copilot delegate command.

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Tagging subscribers to this area: @agocke, @dotnet/illink
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[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 7 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in b0154e0:

• ResultChecker.cs:64-74: replaced Assert.NotNull(exportedType/assemblyRef) with Assert.True(x is not null, $"...") with descriptive messages
• ResultChecker.cs:260: replaced Assert.Equal(expectedExitCode, linkResult.ExitCode) with a conditional Assert.Fail(...) that includes the linker output
• ResultChecker.cs:1209-1212: replaced Assert.Empty(remainingErrors) with Assert.True(!remainingErrors.Any(), ...) including the joined error lines
• IndividualTests.cs:216,251-252: fixed Assert.Equal argument order (expected first, actual second) in all three MVID assertions
• ILTrim.Tests/TestCasesRunner/TestRunner.cs: removed unused using Xunit;
• ParseResponseFileLinesTests.cs:11: removed trailing whitespace

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 4 comments.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in d5455d5:

• ResultChecker.cs:73: changed Single(...) → SingleOrDefault(...) so the subsequent Assert.True(assemblyRef is not null, ...) is reachable and shows the helpful message
• ResultChecker.cs:81-85: same fix — Single(...) → SingleOrDefault(...) + Assert.True(assemblyRef is not null, $"...") with context replacing the redundant Assert.NotNull
• ResultChecker.cs:867-870: replaced Assert.Empty(missingInLinked) with Assert.True(missingInLinked.Count == 0, $"Missing types in linked assembly '{...}': ...")
• ResultChecker.cs:878-880: replaced Assert.Empty(missingMembersInLinked) with Assert.True(missingMembersInLinked.Count == 0, $"Missing members in type '{...}' in linked assembly '{...}': ...")