[test-improver] test: add edge case tests for IgnoreStringMethodReturnValueAnalyzer

[Amaury Levé (Evangelink)]

Goal and Rationale

IgnoreStringMethodReturnValueAnalyzer (MSTEST0055) had only 5 tests, all covering the happy path (diagnostic fires / doesn't fire based on whether the result of Contains, StartsWith, or EndsWith is used). Three distinct code paths in the analyzer's guard logic were completely untested:

Untested path	Guard
Discard assignment _ = str.Contains(...)	expressionStatementOperation.Operation is not IInvocationOperation early return
String method call inside a lambda block body	ExpressionStatement inside lambda — should still fire
String method result used as a receiver in a chained call	IsStringMethodCall on the outer call (not a string method) — should not fire

Approach

Added three [TestMethod] entries to IgnoreStringMethodReturnValueAnalyzerTests.cs:

Test	What it covers
WhenDiscardAssignmentIgnoresReturnValue_NoDiagnostic	_ = str.Contains("Hello") → outer operation is IAssignmentOperation, not IInvocationOperation → early return, no diagnostic
WhenStringMethodReturnValueIgnoredInsideLambda_Diagnostic	() => { str.Contains("Hello"); } → ExpressionStatement inside lambda body triggers diagnostic
WhenStringMethodResultUsedAsReceiverForChainedCall_NoDiagnostic	str.Contains("Hello").GetHashCode() → outermost ExpressionStatement operation is GetHashCode() on System.Boolean, not a string method → no diagnostic on Contains

Trade-offs

Purely additive — no production code changes, no new dependencies.

Test Status

All 8 tests pass (5 existing + 3 new):

Test run summary: Passed!
total: 8
failed: 0
succeeded: 8
duration: 5s 537ms

Reproducibility

.dotnet/dotnet run --project test/UnitTests/MSTest.Analyzers.UnitTests/ -f net8.0 --no-build -- \
--filter "FullyQualifiedName~IgnoreStringMethodReturnValueAnalyzerTests"

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Pull request overview

Adds additional unit-test coverage for the MSTest analyzer IgnoreStringMethodReturnValueAnalyzer (MSTEST0055) to cover previously untested guard/shape scenarios, without changing production analyzer behavior.

Changes:

• Added a test ensuring discard assignments (_ = str.Contains(...)) do not produce MSTEST0055 diagnostics.
• Added a test ensuring ignored string-method return values inside a lambda block body do produce diagnostics.
• Added a test ensuring chained calls where the string method result is used as a receiver (e.g. str.Contains(...).GetHashCode()) do not produce diagnostics.

Show a summary per file

File	Description
test/UnitTests/MSTest.Analyzers.UnitTests/IgnoreStringMethodReturnValueAnalyzerTests.cs	Adds three new test cases covering discard assignment, lambda-body expression statements, and chained-call receiver usage scenarios for MSTEST0055.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Low

[Amaury Levé (Evangelink)]

Note

🤖 Automated review by GitHub Copilot. Posted via a maintainer's GitHub token, so it appears under their account — the account owner did not write or approve this content personally. Generated by the Expert Code Review workflow. To request a follow-up action, reply by tagging @copilot directly.

Expert Review — PR #9468

Reviewed against all 22 dimensions. Changed file: test/UnitTests/MSTest.Analyzers.UnitTests/IgnoreStringMethodReturnValueAnalyzerTests.cs

---

Verdict table

#	Dimension	Result
1	Algorithmic Correctness	✅ LGTM
2	Threading & Concurrency	N/A
3	Security & IPC Contract Safety	N/A
4	Public API & Binary Compatibility	N/A
5	Performance & Allocations	N/A
6	Cross-TFM Compatibility	N/A
7	Resource & IDisposable Management	N/A
8	Defensive Coding at Boundaries	N/A
9	Localization & Resources	N/A
10	Test Isolation	✅ LGTM
11	Assertion Quality	✅ LGTM
12	Flakiness Patterns	✅ LGTM
13	Test Completeness & Coverage	✅ LGTM
14	Data-Driven Test Coverage	N/A
15	Code Structure & Simplification	✅ LGTM
16	Naming & Conventions	⚠️ NIT (see inline)
17	Documentation Accuracy	⚠️ NIT (see inline)
18	Analyzer & Code Fix Quality	✅ LGTM
19	IPC Wire Compatibility	N/A
20	Build Infrastructure & Dependencies	N/A
21	Scope & PR Discipline	✅ LGTM
22	PowerShell Scripting Hygiene	N/A

15/15 applicable dimensions clean. 2 NIT-level findings (no blocking or major issues).

---

Summary

The three new tests correctly target the three distinct guard-logic paths in IgnoreStringMethodReturnValueAnalyzer.AnalyzeExpressionStatement:

Test	Guard path exercised	Verified correct?
WhenDiscardAssignmentIgnoresReturnValue_NoDiagnostic	expressionStatementOperation.Operation is not IInvocationOperation — the outer operation is ISimpleAssignmentOperation (a discard), so early return fires; no diagnostic	✅
WhenStringMethodReturnValueIgnoredInsideLambda_Diagnostic	Block-body lambda still emits an IExpressionStatementOperation; analyzer fires correctly inside the lambda	✅
WhenStringMethodResultUsedAsReceiverForChainedCall_NoDiagnostic	Outer IInvocationOperation is GetHashCode() on System.Boolean, not a string method; IsStringMethodCall returns false	✅

All tests are properly isolated (no shared mutable state, no file system operations), non-flaky, and follow the project's CSharpCodeFixVerifier pattern. The using System; directive is correctly included only where System.Action is needed (the lambda test). No expression-bodied lambda gap exists because () => str.Contains(...) assigned to Action would not compile — the block-body form is the only valid pattern here.

Two NIT-level findings are attached as inline comments (naming precision on line 161, comment precision on line 170). Neither affects correctness or reviewer confidence in the PR.

[Amaury Levé (Evangelink)]

🧪 Test quality grade — PR #9468

3 new test methods graded across 1 file (IgnoreStringMethodReturnValueAnalyzerTests.cs). All three tests earn top marks: they follow a clear Arrange/Act+Assert structure, use VerifyCS.VerifyAnalyzerAsync with and without diagnostic markers to assert both positive and negative analyzer behavior, and carry descriptive names that communicate the scenario and expected outcome. No improvements are needed.

Δ	Test	Grade	Band	Notes
new	IgnoreStringMethodReturnValueAnalyzerTests. WhenExplicitDiscardAssignment_ NoDiagnostic	A	90–100	Clear AAA; verifies the discard-assignment early-return guard produces no false positives.
new	IgnoreStringMethodReturnValueAnalyzerTests. WhenStringMethodResultUsedAsReceiverForChainedCall_ NoDiagnostic	A	90–100	No issues found.
new	IgnoreStringMethodReturnValueAnalyzerTests. WhenStringMethodReturnValueIgnoredInsideLambda_ Diagnostic	A	90–100	No issues found.

_{This advisory comment was generated automatically. Grades are heuristic
and informational — they do not block merging. Re-run with
/grade-tests.}

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