Improve rendering of exception messages when using WithMessage

[dennisdoomen]

In a test like When_one_of_the_types_does_not_match_the_generic_type_it_should_throw_with_a_clear_explanation, a multi-line exception message like this

Expected exception message to match the equivalent of "Expected type to be "System.Int33" because they are of different type, but found "[System.Int32, System.String, System.Int32]".", but "Expected type to be "System.Int32" because they are of different type, but found "[System.Int32, System.String, System.Int32]"." does not.

after this PR, they will be rendered as

Expected exception message to match the equivalent of

    "Expected type to be "System.Int33" because they are of different type, but found "[System.Int32, System.String, System.Int32]".",

but

    "Expected type to be "System.Int32" because they are of different type, but found "[System.Int32, System.String, System.Int32]"."

does not.

[github-actions]

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[coveralls]

Pull Request Test Coverage Report for Build 14133594137

Details

• 68 of 71 (95.77%) changed or added relevant lines in 9 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.03%) to 97.358%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
Src/FluentAssertions/Primitives/StringContainsStrategy.cs	1	4	25.0%

Totals
Change from base Build 14090391235:	-0.03%
Covered Lines:	12442
Relevant Lines:	12637

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💛 - Coveralls

[Copilot]

Pull Request Overview

This PR improves the rendering of exception messages by reformatting multi-line messages and refactoring string comparison and validation methods. Key changes include updating tests to assert multi‐line formatting, renaming and consolidating validation methods across multiple string comparison strategies, and adjusting the trimming behavior in the formatting component.

Reviewed Changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Tests/FluentAssertions.Specs/Exceptions/OuterExceptionSpecs.cs	Added tests to verify multi‐line, long, and short exception message rendering.
Src/FluentAssertions/Specialized/ExceptionAssertions.cs	Refactored exception message assertion logic for clearer output.
Src/FluentAssertions/Primitives/StringWildcardMatchingStrategy.cs	Renamed methods and updated formatting for multi‐line messages.
Src/FluentAssertions/Primitives/StringValidatorSupportingNull.cs	Updated to call the new AssertForEquality method.
Src/FluentAssertions/Primitives/StringValidator.cs	Replaced null validation with a call to AssertNeitherIsNull for better consistency.
Src/FluentAssertions/Primitives/StringStartStrategy.cs	Renamed mismatch validation method and added null checks.
Src/FluentAssertions/Primitives/StringEqualityStrategy.cs	Renamed methods and updated error message formatting.
Src/FluentAssertions/Primitives/StringEndStrategy.cs	Modified error messages and integrated a new null check method.
Src/FluentAssertions/Primitives/StringContainsStrategy.cs	Renamed methods and updated error message parameter ordering.
Src/FluentAssertions/Primitives/IStringComparisonStrategy.cs	Updated the interface to match the new method names.
Src/FluentAssertions/Formatting/Line.cs	Adjusted trimming behavior in ToString to explicitly remove trailing spaces.

Files not reviewed (1)

• Tests/FluentAssertions.Specs/FluentAssertions.Specs.csproj: Language not supported

Comments suppressed due to low confidence (1)

Src/FluentAssertions/Primitives/StringContainsStrategy.cs:25

• [nitpick] Verify that the parameter order in the error message is intentional; currently, 'subject' is passed as the first parameter and 'expected' as the second, which might lead to confusion compared to similar strategies.

                $"Expected {context:string} {0} to contain the equivalent of {1} {expectedOccurrence}{reason}, but found it {actual.Times()}."

[dennisdoomen]

@jnyrup did you not approve or reject the PR on purpose?