Improve assertions error messages with structured format by Evangelink · Pull Request #7444 · microsoft/testfx

Evangelink · 2026-02-20T21:33:12Z

Copilot

Pull request overview

This pull request modernizes assertion error messages by introducing a structured, multi-line format that improves readability and developer experience. The changes replace old-style concatenated messages with formatted parameter displays using raw string literals.

Changes:

Introduced structured error message formatting with parameter names, expressions, and values on separate lines
Added helper methods for value formatting, expression truncation, and redundancy detection
Updated all assertion methods to use the new formatting approach
Removed obsolete resource strings and added new simplified ones
Updated all test expectations to match the new message format

Reviewed changes

Copilot reviewed 41 out of 41 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
Assert.cs	Core formatting infrastructure: FormatValue, FormatParameter, truncation logic
Assert.ThrowsException.cs	Updated to new structured format for exception type mismatches
Assert.StartsWith/EndsWith/Matches.cs	String assertion methods using new format
Assert.IsTrue/IsFalse.cs	Boolean assertion methods with condition parameter display
Assert.IsNull/IsNotNull.cs	Null checking assertions with value display
Assert.IsInstanceOfType/IsExactInstanceOfType.cs	Type checking with structured type comparison
Assert.IComparable.cs	Comparison assertions (greater/less than, positive/negative)
Assert.Count/Contains.cs	Collection assertions with expression parameters
Assert.AreSame.cs	Reference equality with hash code display for disambiguation
FrameworkMessages.resx	Resource string simplification and new message keys
xlf files	Localization files marked with untranslated entries
Test files	Updated expectations for all assertion error messages

test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.IsInstanceOfTypeTests.cs

test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.IsExactInstanceOfTypeTests.cs

test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.AreSame.cs

test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.IsExactInstanceOfTypeTests.cs

test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.Items.cs

test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.IsTrueTests.cs

test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.IsNull.cs

Copilot

Pull request overview

Copilot reviewed 44 out of 44 changed files in this pull request and generated 7 comments.

src/TestFramework/TestFramework/Assertions/Assert.cs

test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.cs

src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.zh-Hans.xlf

src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.pt-BR.xlf

src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.es.xlf

…r messages

Copilot

Pull request overview

Copilot reviewed 44 out of 44 changed files in this pull request and generated no new comments.

nohwnd · 2026-02-23T11:48:04Z

looks great

Copilot

Pull request overview

Copilot reviewed 46 out of 46 changed files in this pull request and generated 4 comments.

test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.cs

test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.StartsWith.cs

Copilot · 2026-02-23T14:08:23Z

test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.MatchesRegex.cs

+    public void MatchesRegex_WhenValueMatchesPattern_ShouldPass()
+        => Assert.MatchesRegex(@"\d+", "abc123");
+
+    public void MatchesRegex_WhenValueDoesNotMatchPattern_ShouldFail()
+    {
+        Action action = () => Assert.MatchesRegex(@"\d+", "abc");
+        action.Should().Throw<AssertFailedException>()
+            .WithMessage("""
+                Assert.MatchesRegex failed.
+                String does not match expected pattern.
+                  pattern: \d+
+                  value: "abc"
+                """);
+    }
+
+    public void DoesNotMatchRegex_WhenValueDoesNotMatchPattern_ShouldPass()
+        => Assert.DoesNotMatchRegex(@"\d+", "abc");
+
+    public void DoesNotMatchRegex_WhenValueMatchesPattern_ShouldFail()
+    {
+        Action action = () => Assert.DoesNotMatchRegex(@"\d+", "abc123");
+        action.Should().Throw<AssertFailedException>()
+            .WithMessage("""
+                Assert.DoesNotMatchRegex failed.
+                String matches pattern but should not.
+                  pattern: \d+
+                  value: "abc123"
+                """);
+    }
+
+    #endregion
+
+    #region MatchesRegex/DoesNotMatchRegex truncation and newline escaping
+
+    public void MatchesRegex_WithLongExpression_ShouldTruncateExpression()
+    {
+        string aVeryLongVariableNameThatExceedsOneHundredCharactersInLengthToTestTruncationBehaviorOfExpressionDisplayXYZ = "hello";
+
+        Action action = () => Assert.MatchesRegex(@"\d+", aVeryLongVariableNameThatExceedsOneHundredCharactersInLengthToTestTruncationBehaviorOfExpressionDisplayXYZ);
+        action.Should().Throw<AssertFailedException>()
+            .WithMessage("""
+                Assert.MatchesRegex failed.
+                String does not match expected pattern.
+                  pattern: \d+
+                  value (aVeryLongVariableNameThatExceedsOneHundredCharactersInLengthToTestTruncationBehaviorOfExpressionDisp...): "hello"
+                """);
+    }
+
+    public void MatchesRegex_WithLongValue_ShouldTruncateValue()
+    {
+        string longValue = new string('x', 300);
+
+        Action action = () => Assert.MatchesRegex(@"\d+", longValue);
+        action.Should().Throw<AssertFailedException>()
+            .WithMessage($"""
+                Assert.MatchesRegex failed.
+                String does not match expected pattern.
+                  pattern: \d+
+                  value (longValue): "{new string('x', 255)}... (302 chars)
+                """);
+    }
+
+    public void MatchesRegex_WithNewlineInValue_ShouldEscapeNewlines()
+    {
+        Action action = () => Assert.MatchesRegex(@"^\d+$", "hello\r\nworld");
+        action.Should().Throw<AssertFailedException>()
+            .WithMessage("""
+                Assert.MatchesRegex failed.
+                String does not match expected pattern.
+                  pattern: ^\d+$
+                  value: "hello\r\nworld"
+                """);
+    }
+
+    public void DoesNotMatchRegex_WithLongExpression_ShouldTruncateExpression()
+    {
+        string aVeryLongVariableNameThatExceedsOneHundredCharactersInLengthToTestTruncationBehaviorOfExpressionDisplayXYZ = "abc123";
+
+        Action action = () => Assert.DoesNotMatchRegex(@"\d+", aVeryLongVariableNameThatExceedsOneHundredCharactersInLengthToTestTruncationBehaviorOfExpressionDisplayXYZ);
+        action.Should().Throw<AssertFailedException>()
+            .WithMessage("""
+                Assert.DoesNotMatchRegex failed.
+                String matches pattern but should not.
+                  pattern: \d+
+                  value (aVeryLongVariableNameThatExceedsOneHundredCharactersInLengthToTestTruncationBehaviorOfExpressionDisp...): "abc123"
+                """);
+    }
+
+    public void DoesNotMatchRegex_WithLongValue_ShouldTruncateValue()
+    {
+        string longValue = new string('1', 300);
+
+        Action action = () => Assert.DoesNotMatchRegex(@"\d+", longValue);
+        action.Should().Throw<AssertFailedException>()
+            .WithMessage($"""
+                Assert.DoesNotMatchRegex failed.
+                String matches pattern but should not.
+                  pattern: \d+
+                  value (longValue): "{new string('1', 255)}... (302 chars)
+                """);
+    }
+
+    public void DoesNotMatchRegex_WithNewlineInValue_ShouldEscapeNewlines()
+    {
+        Action action = () => Assert.DoesNotMatchRegex(@"hello", "hello\r\nworld");
+        action.Should().Throw<AssertFailedException>()
+            .WithMessage("""
+                Assert.DoesNotMatchRegex failed.
+                String matches pattern but should not.
+                  pattern: hello
+                  value: "hello\r\nworld"
+                """);
+    }
+
+    #endregion
+}


All test methods in this new file are missing the [TestMethod] attribute. Without this attribute, none of these tests will be discovered and executed by the test runner.

test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.EndsWith.cs

Copilot AI review requested due to automatic review settings February 20, 2026 21:33

Copilot started reviewing on behalf of Evangelink February 20, 2026 21:33 View session

Copilot AI reviewed Feb 20, 2026

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Add assertion formatting helpers and localized resource strings

8014b3c

Evangelink force-pushed the dev/amauryleve/rework-assert branch 2 times, most recently from a55c762 to 49018c6 Compare February 22, 2026 10:31

Copilot AI review requested due to automatic review settings February 22, 2026 10:31

Copilot started reviewing on behalf of Evangelink February 22, 2026 10:31 View session

Copilot AI reviewed Feb 22, 2026

View reviewed changes

Evangelink added 14 commits February 22, 2026 11:37

Improve AreEqual/AreNotEqual assertion error messages

b2127af

Improve AreSame/AreNotSame assertion error messages

9ac4849

Improve IsTrue/IsFalse assertion error messages

375f0b5

Improve IsNull/IsNotNull assertion error messages

bd66356

Improve IsInstanceOfType/IsNotInstanceOfType assertion error messages

7e7f07e

Improve IsExactInstanceOfType/IsNotExactInstanceOfType assertion erro…

bebe2ef

…r messages

Improve IComparable assertion error messages

d35c33b

Improve HasCount/IsEmpty/IsNotEmpty assertion error messages

23758d2

Improve ThrowsException assertion error messages

3705c74

Improve Contains/DoesNotContain/IsInRange assertion error messages

23cd627

Improve StartsWith/DoesNotStartWith assertion error messages

dd88189

Improve EndsWith/DoesNotEndWith assertion error messages

0c10f63

Improve MatchesRegex/DoesNotMatchRegex assertion error messages

14a6ec3

Minor test cleanup for Inconclusive assertion

63e8257

Evangelink force-pushed the dev/amauryleve/rework-assert branch from 49018c6 to 63e8257 Compare February 22, 2026 10:38

Address Copilot feedback

f559387

Copilot AI review requested due to automatic review settings February 22, 2026 12:56

Copilot started reviewing on behalf of Evangelink February 22, 2026 12:56 View session

Copilot AI reviewed Feb 22, 2026

View reviewed changes

Fix acceptance tests

dfe9891

Evangelink marked this pull request as ready for review February 23, 2026 14:05

Copilot AI review requested due to automatic review settings February 23, 2026 14:05

Copilot started reviewing on behalf of Evangelink February 23, 2026 14:06 View session

Copilot AI reviewed Feb 23, 2026

View reviewed changes

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nohwnd commented Feb 23, 2026

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Evangelink commented Feb 20, 2026 •

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