Render BCL values with full precision in assertion failure messages

[Amaury Levé (Evangelink)]

Fixes#8963.

Problem

The structured assertion messages introduced by RFC-012 render values via AssertionValueRenderer.RenderValue, which previously fell back to value.ToString() for any type other than string/bool/char/IEnumerable. For many BCL types this collapses the precision the assertion was actually comparing, making failures hard to interpret. For example, when comparing two DateTime values that differ by a few ticks, both expected and actual were rendered as the same 2026-06-09T13:12:21 string.

Fix

Add type-specific, full-precision, culture-invariant arms to the central RenderValue switch:

Type	Format	Notes
DateTime	O	Round-trip, 7 fractional digits, preserves Kind
DateTimeOffset	O	Round-trip, preserves offset
TimeSpan	c	Constant invariant format
DateOnly, TimeOnly	O	Gated #if NET6_0_OR_GREATER
float, double	R	Round-trip, distinguishes adjacent bit patterns
decimal	default	Already lossless; just forces InvariantCulture

All formatting uses CultureInfo.InvariantCulture so messages are reproducible regardless of the runner's locale (e.g. fr-FR no longer renders doubles with comma separators).

Because every public assertion API that surfaces values through structured messages funnels through this single renderer, the fix is centralized and covers AreEqual, AreNotEqual, AreEqual with delta, AreSequenceEqual, Contains, ContainsAll, DoesNotContain, IsInRange, IsGreaterThan, IsLessThan, AreEquivalent, etc.

Tests

• Renderer-level (AssertionValueRendererTests): added ~20 tests covering all new branches — ticks-apart DateTime, UTC Kind, fractional-second TimeSpan, DateOnly/TimeOnly (NET6+), double NaN/Infinity/precision/invariant culture, float adjacent bit patterns, decimal invariant culture, and rendering inside collections. Float adjacent-bit construction uses BitConverter.GetBytes/ToUInt32/ToSingle so it works on net48.
• End-to-end (AssertTests.RenderingPrecision.cs): a new AssertTests partial asserting failure-message contents for the impacted public APIs — Assert.AreEqual/AreNotEqual on DateTime/DateTimeOffset/double (incl. fr-FR)/float (adjacent-bit)/TimeSpan/decimal (fr-FR)/TimeOnly/DateOnly, AreEqual<double> with delta, IsInRange<DateTime>, IsGreaterThan<DateTime>, Contains<DateTime>, ContainsAll<DateTime>, AreSequenceEqual<DateTime>.

All 1,226 / 1,219 (net48) tests in TestFramework.UnitTests pass on net48, net8.0, and net9.0.

[Copilot]

Pull request overview

This PR improves MSTest’s structured assertion failure messages by rendering common BCL value types with full precision and using InvariantCulture, ensuring expected/actual values don’t collapse to indistinguishable text (fixes #8963).

Changes:

• Extend AssertionValueRenderer.RenderValue with type-specific, full-precision, culture-invariant formatting for DateTime, DateTimeOffset, TimeSpan, float, double, decimal (and DateOnly/TimeOnly on NET6+).
• Add renderer-level unit tests covering the new formatting branches and culture invariance.
• Add end-to-end assertion tests validating failure-message contents for multiple public Assert APIs.

Show a summary per file

File	Description
src/TestFramework/TestFramework/Assertions/AssertionValueRenderer.cs	Adds invariant, full-precision formatting arms for key BCL types in the central renderer.
test/UnitTests/TestFramework.UnitTests/Assertions/AssertionValueRendererTests.cs	Expands unit coverage for new renderer behavior (precision, special floating values, invariant culture, NET6+ types, collections).
test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.RenderingPrecision.cs	Adds regression tests that validate failure messages across key assertion APIs now render BCL values with full precision.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 1

[Amaury Levé (Evangelink)]

Fixes#8963.

Problem

The structured assertion messages introduced by RFC-012 render values via AssertionValueRenderer.RenderValue, which previously fell back to value.ToString() for any type other than string/bool/char/IEnumerable. For many BCL types this collapses the precision the assertion was actually comparing, making failures hard to interpret. For example, when comparing two DateTime values that differ by a few ticks, both expected and actual were rendered as the same 2026-06-09T13:12:21 string.

Fix

Add type-specific, full-precision, culture-invariant arms to the central RenderValue switch:

Type	Format	Notes
DateTime	O	Round-trip, 7 fractional digits, preserves Kind
DateTimeOffset	O	Round-trip, preserves offset
TimeSpan	c	Constant invariant format
DateOnly, TimeOnly	O	Gated #if NET6_0_OR_GREATER
float, double	R	Round-trip, distinguishes adjacent bit patterns
decimal	default	Already lossless; just forces InvariantCulture

All formatting uses CultureInfo.InvariantCulture so messages are reproducible regardless of the runner's locale (e.g. fr-FR no longer renders doubles with comma separators).

Because every public assertion API that surfaces values through structured messages funnels through this single renderer, the fix is centralized and covers AreEqual, AreNotEqual, AreEqual with delta, AreSequenceEqual, Contains, ContainsAll, DoesNotContain, IsInRange, IsGreaterThan, IsLessThan, AreEquivalent, etc.

Tests

• Renderer-level (AssertionValueRendererTests): added ~20 tests covering all new branches — ticks-apart DateTime, UTC Kind, fractional-second TimeSpan, DateOnly/TimeOnly (NET6+), double NaN/Infinity/precision/invariant culture, float adjacent bit patterns, decimal invariant culture, and rendering inside collections. Float adjacent-bit construction uses BitConverter.GetBytes/ToUInt32/ToSingle so it works on net48.
• End-to-end (AssertTests.RenderingPrecision.cs): a new AssertTests partial asserting failure-message contents for the impacted public APIs — Assert.AreEqual/AreNotEqual on DateTime/DateTimeOffset/double (incl. fr-FR)/float (adjacent-bit)/TimeSpan/decimal (fr-FR)/TimeOnly/DateOnly, AreEqual<double> with delta, IsInRange<DateTime>, IsGreaterThan<DateTime>, Contains<DateTime>, ContainsAll<DateTime>, AreSequenceEqual<DateTime>.

All 1,226 / 1,219 (net48) tests in TestFramework.UnitTests pass on net48, net8.0, and net9.0.

[Copilot]

Pull request overview

This PR improves MSTest’s structured assertion failure messages by rendering common BCL value types with full precision and using InvariantCulture, ensuring expected/actual values don’t collapse to indistinguishable text (fixes #8963).

Changes:

• Extend AssertionValueRenderer.RenderValue with type-specific, full-precision, culture-invariant formatting for DateTime, DateTimeOffset, TimeSpan, float, double, decimal (and DateOnly/TimeOnly on NET6+).
• Add renderer-level unit tests covering the new formatting branches and culture invariance.
• Add end-to-end assertion tests validating failure-message contents for multiple public Assert APIs.

Show a summary per file

File	Description
src/TestFramework/TestFramework/Assertions/AssertionValueRenderer.cs	Adds invariant, full-precision formatting arms for key BCL types in the central renderer.
test/UnitTests/TestFramework.UnitTests/Assertions/AssertionValueRendererTests.cs	Expands unit coverage for new renderer behavior (precision, special floating values, invariant culture, NET6+ types, collections).
test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.RenderingPrecision.cs	Adds regression tests that validate failure messages across key assertion APIs now render BCL values with full precision.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 1

[Amaury Levé (Evangelink)]

Fixes#8963.

Problem

The structured assertion messages introduced by RFC-012 render values via AssertionValueRenderer.RenderValue, which previously fell back to value.ToString() for any type other than string/bool/char/IEnumerable. For many BCL types this collapses the precision the assertion was actually comparing, making failures hard to interpret. For example, when comparing two DateTime values that differ by a few ticks, both expected and actual were rendered as the same 2026-06-09T13:12:21 string.

Fix

Add type-specific, full-precision, culture-invariant arms to the central RenderValue switch:

Type	Format	Notes
DateTime	O	Round-trip, 7 fractional digits, preserves Kind
DateTimeOffset	O	Round-trip, preserves offset
TimeSpan	c	Constant invariant format
DateOnly, TimeOnly	O	Gated #if NET6_0_OR_GREATER
float, double	R	Round-trip, distinguishes adjacent bit patterns
decimal	default	Already lossless; just forces InvariantCulture

All formatting uses CultureInfo.InvariantCulture so messages are reproducible regardless of the runner's locale (e.g. fr-FR no longer renders doubles with comma separators).

Because every public assertion API that surfaces values through structured messages funnels through this single renderer, the fix is centralized and covers AreEqual, AreNotEqual, AreEqual with delta, AreSequenceEqual, Contains, ContainsAll, DoesNotContain, IsInRange, IsGreaterThan, IsLessThan, AreEquivalent, etc.

Tests

• Renderer-level (AssertionValueRendererTests): added ~20 tests covering all new branches — ticks-apart DateTime, UTC Kind, fractional-second TimeSpan, DateOnly/TimeOnly (NET6+), double NaN/Infinity/precision/invariant culture, float adjacent bit patterns, decimal invariant culture, and rendering inside collections. Float adjacent-bit construction uses BitConverter.GetBytes/ToUInt32/ToSingle so it works on net48.
• End-to-end (AssertTests.RenderingPrecision.cs): a new AssertTests partial asserting failure-message contents for the impacted public APIs — Assert.AreEqual/AreNotEqual on DateTime/DateTimeOffset/double (incl. fr-FR)/float (adjacent-bit)/TimeSpan/decimal (fr-FR)/TimeOnly/DateOnly, AreEqual<double> with delta, IsInRange<DateTime>, IsGreaterThan<DateTime>, Contains<DateTime>, ContainsAll<DateTime>, AreSequenceEqual<DateTime>.

All 1,226 / 1,219 (net48) tests in TestFramework.UnitTests pass on net48, net8.0, and net9.0.

[Copilot]

Pull request overview

This PR improves MSTest’s structured assertion failure messages by rendering common BCL value types with full precision and using InvariantCulture, ensuring expected/actual values don’t collapse to indistinguishable text (fixes #8963).

Changes:

• Extend AssertionValueRenderer.RenderValue with type-specific, full-precision, culture-invariant formatting for DateTime, DateTimeOffset, TimeSpan, float, double, decimal (and DateOnly/TimeOnly on NET6+).
• Add renderer-level unit tests covering the new formatting branches and culture invariance.
• Add end-to-end assertion tests validating failure-message contents for multiple public Assert APIs.

Show a summary per file

File	Description
src/TestFramework/TestFramework/Assertions/AssertionValueRenderer.cs	Adds invariant, full-precision formatting arms for key BCL types in the central renderer.
test/UnitTests/TestFramework.UnitTests/Assertions/AssertionValueRendererTests.cs	Expands unit coverage for new renderer behavior (precision, special floating values, invariant culture, NET6+ types, collections).
test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.RenderingPrecision.cs	Adds regression tests that validate failure messages across key assertion APIs now render BCL values with full precision.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 1

[Amaury Levé (Evangelink)]

Fixes#8963.

Problem

The structured assertion messages introduced by RFC-012 render values via AssertionValueRenderer.RenderValue, which previously fell back to value.ToString() for any type other than string/bool/char/IEnumerable. For many BCL types this collapses the precision the assertion was actually comparing, making failures hard to interpret. For example, when comparing two DateTime values that differ by a few ticks, both expected and actual were rendered as the same 2026-06-09T13:12:21 string.

Fix

Add type-specific, full-precision, culture-invariant arms to the central RenderValue switch:

Type	Format	Notes
DateTime	O	Round-trip, 7 fractional digits, preserves Kind
DateTimeOffset	O	Round-trip, preserves offset
TimeSpan	c	Constant invariant format
DateOnly, TimeOnly	O	Gated #if NET6_0_OR_GREATER
float, double	R	Round-trip, distinguishes adjacent bit patterns
decimal	default	Already lossless; just forces InvariantCulture

All formatting uses CultureInfo.InvariantCulture so messages are reproducible regardless of the runner's locale (e.g. fr-FR no longer renders doubles with comma separators).

Because every public assertion API that surfaces values through structured messages funnels through this single renderer, the fix is centralized and covers AreEqual, AreNotEqual, AreEqual with delta, AreSequenceEqual, Contains, ContainsAll, DoesNotContain, IsInRange, IsGreaterThan, IsLessThan, AreEquivalent, etc.

Tests

• Renderer-level (AssertionValueRendererTests): added ~20 tests covering all new branches — ticks-apart DateTime, UTC Kind, fractional-second TimeSpan, DateOnly/TimeOnly (NET6+), double NaN/Infinity/precision/invariant culture, float adjacent bit patterns, decimal invariant culture, and rendering inside collections. Float adjacent-bit construction uses BitConverter.GetBytes/ToUInt32/ToSingle so it works on net48.
• End-to-end (AssertTests.RenderingPrecision.cs): a new AssertTests partial asserting failure-message contents for the impacted public APIs — Assert.AreEqual/AreNotEqual on DateTime/DateTimeOffset/double (incl. fr-FR)/float (adjacent-bit)/TimeSpan/decimal (fr-FR)/TimeOnly/DateOnly, AreEqual<double> with delta, IsInRange<DateTime>, IsGreaterThan<DateTime>, Contains<DateTime>, ContainsAll<DateTime>, AreSequenceEqual<DateTime>.

All 1,226 / 1,219 (net48) tests in TestFramework.UnitTests pass on net48, net8.0, and net9.0.

[Copilot]

Pull request overview

This PR improves MSTest’s structured assertion failure messages by rendering common BCL value types with full precision and using InvariantCulture, ensuring expected/actual values don’t collapse to indistinguishable text (fixes #8963).

Changes:

• Extend AssertionValueRenderer.RenderValue with type-specific, full-precision, culture-invariant formatting for DateTime, DateTimeOffset, TimeSpan, float, double, decimal (and DateOnly/TimeOnly on NET6+).
• Add renderer-level unit tests covering the new formatting branches and culture invariance.
• Add end-to-end assertion tests validating failure-message contents for multiple public Assert APIs.

Show a summary per file

File	Description
src/TestFramework/TestFramework/Assertions/AssertionValueRenderer.cs	Adds invariant, full-precision formatting arms for key BCL types in the central renderer.
test/UnitTests/TestFramework.UnitTests/Assertions/AssertionValueRendererTests.cs	Expands unit coverage for new renderer behavior (precision, special floating values, invariant culture, NET6+ types, collections).
test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.RenderingPrecision.cs	Adds regression tests that validate failure messages across key assertion APIs now render BCL values with full precision.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 1

[Amaury Levé (Evangelink)]

Fixes#8963.

Problem

The structured assertion messages introduced by RFC-012 render values via AssertionValueRenderer.RenderValue, which previously fell back to value.ToString() for any type other than string/bool/char/IEnumerable. For many BCL types this collapses the precision the assertion was actually comparing, making failures hard to interpret. For example, when comparing two DateTime values that differ by a few ticks, both expected and actual were rendered as the same 2026-06-09T13:12:21 string.

Fix

Add type-specific, full-precision, culture-invariant arms to the central RenderValue switch:

Type	Format	Notes
DateTime	O	Round-trip, 7 fractional digits, preserves Kind
DateTimeOffset	O	Round-trip, preserves offset
TimeSpan	c	Constant invariant format
DateOnly, TimeOnly	O	Gated #if NET6_0_OR_GREATER
float, double	R	Round-trip, distinguishes adjacent bit patterns
decimal	default	Already lossless; just forces InvariantCulture

All formatting uses CultureInfo.InvariantCulture so messages are reproducible regardless of the runner's locale (e.g. fr-FR no longer renders doubles with comma separators).

Because every public assertion API that surfaces values through structured messages funnels through this single renderer, the fix is centralized and covers AreEqual, AreNotEqual, AreEqual with delta, AreSequenceEqual, Contains, ContainsAll, DoesNotContain, IsInRange, IsGreaterThan, IsLessThan, AreEquivalent, etc.

Tests

• Renderer-level (AssertionValueRendererTests): added ~20 tests covering all new branches — ticks-apart DateTime, UTC Kind, fractional-second TimeSpan, DateOnly/TimeOnly (NET6+), double NaN/Infinity/precision/invariant culture, float adjacent bit patterns, decimal invariant culture, and rendering inside collections. Float adjacent-bit construction uses BitConverter.GetBytes/ToUInt32/ToSingle so it works on net48.
• End-to-end (AssertTests.RenderingPrecision.cs): a new AssertTests partial asserting failure-message contents for the impacted public APIs — Assert.AreEqual/AreNotEqual on DateTime/DateTimeOffset/double (incl. fr-FR)/float (adjacent-bit)/TimeSpan/decimal (fr-FR)/TimeOnly/DateOnly, AreEqual<double> with delta, IsInRange<DateTime>, IsGreaterThan<DateTime>, Contains<DateTime>, ContainsAll<DateTime>, AreSequenceEqual<DateTime>.

All 1,226 / 1,219 (net48) tests in TestFramework.UnitTests pass on net48, net8.0, and net9.0.

[Copilot]

Pull request overview

This PR improves MSTest’s structured assertion failure messages by rendering common BCL value types with full precision and using InvariantCulture, ensuring expected/actual values don’t collapse to indistinguishable text (fixes #8963).

Changes:

• Extend AssertionValueRenderer.RenderValue with type-specific, full-precision, culture-invariant formatting for DateTime, DateTimeOffset, TimeSpan, float, double, decimal (and DateOnly/TimeOnly on NET6+).
• Add renderer-level unit tests covering the new formatting branches and culture invariance.
• Add end-to-end assertion tests validating failure-message contents for multiple public Assert APIs.

Show a summary per file

File	Description
src/TestFramework/TestFramework/Assertions/AssertionValueRenderer.cs	Adds invariant, full-precision formatting arms for key BCL types in the central renderer.
test/UnitTests/TestFramework.UnitTests/Assertions/AssertionValueRendererTests.cs	Expands unit coverage for new renderer behavior (precision, special floating values, invariant culture, NET6+ types, collections).
test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.RenderingPrecision.cs	Adds regression tests that validate failure messages across key assertion APIs now render BCL values with full precision.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 1

[Amaury Levé (Evangelink)]

Fixes#8963.

Problem

The structured assertion messages introduced by RFC-012 render values via AssertionValueRenderer.RenderValue, which previously fell back to value.ToString() for any type other than string/bool/char/IEnumerable. For many BCL types this collapses the precision the assertion was actually comparing, making failures hard to interpret. For example, when comparing two DateTime values that differ by a few ticks, both expected and actual were rendered as the same 2026-06-09T13:12:21 string.

Fix

Add type-specific, full-precision, culture-invariant arms to the central RenderValue switch:

Type	Format	Notes
DateTime	O	Round-trip, 7 fractional digits, preserves Kind
DateTimeOffset	O	Round-trip, preserves offset
TimeSpan	c	Constant invariant format
DateOnly, TimeOnly	O	Gated #if NET6_0_OR_GREATER
float, double	R	Round-trip, distinguishes adjacent bit patterns
decimal	default	Already lossless; just forces InvariantCulture

All formatting uses CultureInfo.InvariantCulture so messages are reproducible regardless of the runner's locale (e.g. fr-FR no longer renders doubles with comma separators).

Because every public assertion API that surfaces values through structured messages funnels through this single renderer, the fix is centralized and covers AreEqual, AreNotEqual, AreEqual with delta, AreSequenceEqual, Contains, ContainsAll, DoesNotContain, IsInRange, IsGreaterThan, IsLessThan, AreEquivalent, etc.

Tests

• Renderer-level (AssertionValueRendererTests): added ~20 tests covering all new branches — ticks-apart DateTime, UTC Kind, fractional-second TimeSpan, DateOnly/TimeOnly (NET6+), double NaN/Infinity/precision/invariant culture, float adjacent bit patterns, decimal invariant culture, and rendering inside collections. Float adjacent-bit construction uses BitConverter.GetBytes/ToUInt32/ToSingle so it works on net48.
• End-to-end (AssertTests.RenderingPrecision.cs): a new AssertTests partial asserting failure-message contents for the impacted public APIs — Assert.AreEqual/AreNotEqual on DateTime/DateTimeOffset/double (incl. fr-FR)/float (adjacent-bit)/TimeSpan/decimal (fr-FR)/TimeOnly/DateOnly, AreEqual<double> with delta, IsInRange<DateTime>, IsGreaterThan<DateTime>, Contains<DateTime>, ContainsAll<DateTime>, AreSequenceEqual<DateTime>.

All 1,226 / 1,219 (net48) tests in TestFramework.UnitTests pass on net48, net8.0, and net9.0.

[Copilot]

Pull request overview

This PR improves MSTest’s structured assertion failure messages by rendering common BCL value types with full precision and using InvariantCulture, ensuring expected/actual values don’t collapse to indistinguishable text (fixes #8963).

Changes:

• Extend AssertionValueRenderer.RenderValue with type-specific, full-precision, culture-invariant formatting for DateTime, DateTimeOffset, TimeSpan, float, double, decimal (and DateOnly/TimeOnly on NET6+).
• Add renderer-level unit tests covering the new formatting branches and culture invariance.
• Add end-to-end assertion tests validating failure-message contents for multiple public Assert APIs.

Show a summary per file

File	Description
src/TestFramework/TestFramework/Assertions/AssertionValueRenderer.cs	Adds invariant, full-precision formatting arms for key BCL types in the central renderer.
test/UnitTests/TestFramework.UnitTests/Assertions/AssertionValueRendererTests.cs	Expands unit coverage for new renderer behavior (precision, special floating values, invariant culture, NET6+ types, collections).
test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.RenderingPrecision.cs	Adds regression tests that validate failure messages across key assertion APIs now render BCL values with full precision.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 1

[Amaury Levé (Evangelink)]

Fixes#8963.

Problem

The structured assertion messages introduced by RFC-012 render values via AssertionValueRenderer.RenderValue, which previously fell back to value.ToString() for any type other than string/bool/char/IEnumerable. For many BCL types this collapses the precision the assertion was actually comparing, making failures hard to interpret. For example, when comparing two DateTime values that differ by a few ticks, both expected and actual were rendered as the same 2026-06-09T13:12:21 string.

Fix

Add type-specific, full-precision, culture-invariant arms to the central RenderValue switch:

Type	Format	Notes
DateTime	O	Round-trip, 7 fractional digits, preserves Kind
DateTimeOffset	O	Round-trip, preserves offset
TimeSpan	c	Constant invariant format
DateOnly, TimeOnly	O	Gated #if NET6_0_OR_GREATER
float, double	R	Round-trip, distinguishes adjacent bit patterns
decimal	default	Already lossless; just forces InvariantCulture

All formatting uses CultureInfo.InvariantCulture so messages are reproducible regardless of the runner's locale (e.g. fr-FR no longer renders doubles with comma separators).

Because every public assertion API that surfaces values through structured messages funnels through this single renderer, the fix is centralized and covers AreEqual, AreNotEqual, AreEqual with delta, AreSequenceEqual, Contains, ContainsAll, DoesNotContain, IsInRange, IsGreaterThan, IsLessThan, AreEquivalent, etc.

Tests

• Renderer-level (AssertionValueRendererTests): added ~20 tests covering all new branches — ticks-apart DateTime, UTC Kind, fractional-second TimeSpan, DateOnly/TimeOnly (NET6+), double NaN/Infinity/precision/invariant culture, float adjacent bit patterns, decimal invariant culture, and rendering inside collections. Float adjacent-bit construction uses BitConverter.GetBytes/ToUInt32/ToSingle so it works on net48.
• End-to-end (AssertTests.RenderingPrecision.cs): a new AssertTests partial asserting failure-message contents for the impacted public APIs — Assert.AreEqual/AreNotEqual on DateTime/DateTimeOffset/double (incl. fr-FR)/float (adjacent-bit)/TimeSpan/decimal (fr-FR)/TimeOnly/DateOnly, AreEqual<double> with delta, IsInRange<DateTime>, IsGreaterThan<DateTime>, Contains<DateTime>, ContainsAll<DateTime>, AreSequenceEqual<DateTime>.

All 1,226 / 1,219 (net48) tests in TestFramework.UnitTests pass on net48, net8.0, and net9.0.

[Copilot]

Pull request overview

This PR improves MSTest’s structured assertion failure messages by rendering common BCL value types with full precision and using InvariantCulture, ensuring expected/actual values don’t collapse to indistinguishable text (fixes #8963).

Changes:

• Extend AssertionValueRenderer.RenderValue with type-specific, full-precision, culture-invariant formatting for DateTime, DateTimeOffset, TimeSpan, float, double, decimal (and DateOnly/TimeOnly on NET6+).
• Add renderer-level unit tests covering the new formatting branches and culture invariance.
• Add end-to-end assertion tests validating failure-message contents for multiple public Assert APIs.

Show a summary per file

File	Description
src/TestFramework/TestFramework/Assertions/AssertionValueRenderer.cs	Adds invariant, full-precision formatting arms for key BCL types in the central renderer.
test/UnitTests/TestFramework.UnitTests/Assertions/AssertionValueRendererTests.cs	Expands unit coverage for new renderer behavior (precision, special floating values, invariant culture, NET6+ types, collections).
test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.RenderingPrecision.cs	Adds regression tests that validate failure messages across key assertion APIs now render BCL values with full precision.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 1

[Amaury Levé (Evangelink)]

Fixes#8963.

Problem

The structured assertion messages introduced by RFC-012 render values via AssertionValueRenderer.RenderValue, which previously fell back to value.ToString() for any type other than string/bool/char/IEnumerable. For many BCL types this collapses the precision the assertion was actually comparing, making failures hard to interpret. For example, when comparing two DateTime values that differ by a few ticks, both expected and actual were rendered as the same 2026-06-09T13:12:21 string.

Fix

Add type-specific, full-precision, culture-invariant arms to the central RenderValue switch:

Type	Format	Notes
DateTime	O	Round-trip, 7 fractional digits, preserves Kind
DateTimeOffset	O	Round-trip, preserves offset
TimeSpan	c	Constant invariant format
DateOnly, TimeOnly	O	Gated #if NET6_0_OR_GREATER
float, double	R	Round-trip, distinguishes adjacent bit patterns
decimal	default	Already lossless; just forces InvariantCulture

All formatting uses CultureInfo.InvariantCulture so messages are reproducible regardless of the runner's locale (e.g. fr-FR no longer renders doubles with comma separators).

Because every public assertion API that surfaces values through structured messages funnels through this single renderer, the fix is centralized and covers AreEqual, AreNotEqual, AreEqual with delta, AreSequenceEqual, Contains, ContainsAll, DoesNotContain, IsInRange, IsGreaterThan, IsLessThan, AreEquivalent, etc.

Tests

• Renderer-level (AssertionValueRendererTests): added ~20 tests covering all new branches — ticks-apart DateTime, UTC Kind, fractional-second TimeSpan, DateOnly/TimeOnly (NET6+), double NaN/Infinity/precision/invariant culture, float adjacent bit patterns, decimal invariant culture, and rendering inside collections. Float adjacent-bit construction uses BitConverter.GetBytes/ToUInt32/ToSingle so it works on net48.
• End-to-end (AssertTests.RenderingPrecision.cs): a new AssertTests partial asserting failure-message contents for the impacted public APIs — Assert.AreEqual/AreNotEqual on DateTime/DateTimeOffset/double (incl. fr-FR)/float (adjacent-bit)/TimeSpan/decimal (fr-FR)/TimeOnly/DateOnly, AreEqual<double> with delta, IsInRange<DateTime>, IsGreaterThan<DateTime>, Contains<DateTime>, ContainsAll<DateTime>, AreSequenceEqual<DateTime>.

All 1,226 / 1,219 (net48) tests in TestFramework.UnitTests pass on net48, net8.0, and net9.0.

[Copilot]

Pull request overview

This PR improves MSTest’s structured assertion failure messages by rendering common BCL value types with full precision and using InvariantCulture, ensuring expected/actual values don’t collapse to indistinguishable text (fixes #8963).

Changes:

• Extend AssertionValueRenderer.RenderValue with type-specific, full-precision, culture-invariant formatting for DateTime, DateTimeOffset, TimeSpan, float, double, decimal (and DateOnly/TimeOnly on NET6+).
• Add renderer-level unit tests covering the new formatting branches and culture invariance.
• Add end-to-end assertion tests validating failure-message contents for multiple public Assert APIs.

Show a summary per file

File	Description
src/TestFramework/TestFramework/Assertions/AssertionValueRenderer.cs	Adds invariant, full-precision formatting arms for key BCL types in the central renderer.
test/UnitTests/TestFramework.UnitTests/Assertions/AssertionValueRendererTests.cs	Expands unit coverage for new renderer behavior (precision, special floating values, invariant culture, NET6+ types, collections).
test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.RenderingPrecision.cs	Adds regression tests that validate failure messages across key assertion APIs now render BCL values with full precision.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 1