Apply structured assertion messages (RFC 012) to Assert.Contains family

[Evangelink]

Continues the rollout of RFC 012 — Structured Assertion Messages by migrating the Assert Contains family to the structured-message format. Follows the patterns established by previously merged work (#8170, #8187, #8210, #8214) and the in-flight series (#8258, #8259, #8260, #8262).

APIs migrated

• Assert.ContainsSingle (collection-only and predicate overloads, including the interpolated-string-handler)
• Assert.Contains (item, predicate, substring overloads, with optional comparer / StringComparison)
• Assert.DoesNotContain (item, predicate, substring overloads, with optional comparer / StringComparison)
• Assert.IsInRange

Output format

Assert.ContainsSingle(new[] { 1, 2, 3 }):

Assertion failed. Expected collection to contain exactly one element.

expected count: 1
actual count:   3

Assert.ContainsSingle(new[] { 1, 2, 3 })

Assert.Contains(20, collection, ""Item 20 not found""):

Assertion failed. Expected collection to contain the specified element.
Item 20 not found

expected: 20

Assert.Contains(20, collection)

Assert.DoesNotContain(""brown"", ""The quick brown fox"", StringComparison.Ordinal, ""Unexpected substring""):

Assertion failed. Expected string to not contain the specified substring.
Unexpected substring

unexpected substring: ""brown""
actual:               ""The quick brown fox""
comparison:           Ordinal

Assert.DoesNotContain(substring, value)

Assert.IsInRange(1, 5, 10, ""Custom error message""):

Assertion failed. Expected value to be within the inclusive range.
Custom error message

expected: [1, 5]
actual:   10

Assert.IsInRange(minValue, maxValue, value)

Notes

• Adds nine new *FailedSummary resource entries for ContainsSingle, ContainsSingleMatch, ContainsItem, ContainsPredicate, ContainsSubstring, DoesNotContainItem, DoesNotContainPredicate, DoesNotContainSubstring, IsInRange (XLF files regenerated via UpdateXlf).
• A comparer: line is added to the evidence block when an item-based Contains/DoesNotContain is invoked with a non-default IEqualityComparer/IEqualityComparer<T>.
• IsInRange uses a small custom call-site formatter so all three captured arguments (minValue, maxValue, value) appear in the call-site line.
• Removes the now-unused BuildUserMessageForSubstringExpression*, BuildUserMessageForExpected/NotExpected/Predicate*CollectionExpression, BuildUserMessageForMinValue*MaxValue*Value*, and BuildUserMessageForThreeExpressions helpers from Assert.cs.
• Updates the affected message-format tests in AssertTests.Contains.cs, AssertTests.IsInRange.cs, AssertTests.Items.cs (ContainsSingle scenarios), and AssertTests.ScopeTests.cs.

Validation

• dotnet build src/TestFramework/TestFramework/TestFramework.csproj -c Debug — clean.
• dotnet test test/UnitTests/TestFramework.UnitTests/TestFramework.UnitTests.csproj -c Debug — 3535/3535 passed.

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

[Copilot]

Pull request overview

This PR continues the RFC 012 “Structured Assertion Messages” rollout by migrating the Assert.Contains* family (ContainsSingle, Contains, DoesNotContain, and IsInRange) from legacy single-line messages to the structured multi-line message format, including new localized resource summary entries and updated unit-test expectations.

Changes:

• Reworked Assert.Contains*/Assert.DoesNotContain*/Assert.ContainsSingle* failure paths to build StructuredAssertionMessage instances (summary + optional user message + evidence + call-site).
• Migrated Assert.IsInRange failures to structured messages, including a custom call-site formatter that preserves all 3 arguments.
• Added new *FailedSummary resource keys and regenerated XLF entries; updated affected message-format unit tests.

Show a summary per file

File	Description
test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.ScopeTests.cs	Updates soft-assert (AssertScope) expectations for ContainsSingle to structured message output.
test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.Items.cs	Updates ContainsSingle unit tests to match structured message formatting.
test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.IsInRange.cs	Updates IsInRange unit tests to assert on structured evidence/summary content.
test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.Contains.cs	Updates Contains/DoesNotContain/ContainsSingle unit tests to match structured failure messages.
src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.zh-Hant.xlf	Adds new *FailedSummary trans-units for structured assertion summaries.
src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.zh-Hans.xlf	Adds new *FailedSummary trans-units for structured assertion summaries.
src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.tr.xlf	Adds new *FailedSummary trans-units for structured assertion summaries.
src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.ru.xlf	Adds new *FailedSummary trans-units for structured assertion summaries.
src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.pt-BR.xlf	Adds new *FailedSummary trans-units for structured assertion summaries.
src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.pl.xlf	Adds new *FailedSummary trans-units for structured assertion summaries.
src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.ko.xlf	Adds new *FailedSummary trans-units for structured assertion summaries.
src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.ja.xlf	Adds new *FailedSummary trans-units for structured assertion summaries.
src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.it.xlf	Adds new *FailedSummary trans-units for structured assertion summaries.
src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.fr.xlf	Adds new *FailedSummary trans-units for structured assertion summaries.
src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.es.xlf	Adds new *FailedSummary trans-units for structured assertion summaries.
src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.de.xlf	Adds new *FailedSummary trans-units for structured assertion summaries.
src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.cs.xlf	Adds new *FailedSummary trans-units for structured assertion summaries.
src/TestFramework/TestFramework/Resources/FrameworkMessages.resx	Adds new *FailedSummary resource entries backing structured summaries for migrated assertions.
src/TestFramework/TestFramework/Assertions/Assert.cs	Removes now-unused legacy “BuildUserMessageForExpression” helpers.
src/TestFramework/TestFramework/Assertions/Assert.Contains.cs	Core migration: converts Contains*/DoesNotContain*/ContainsSingle*/IsInRange failure reporting to structured message builders.

Copilot's findings

Comments suppressed due to low confidence (1)

src/TestFramework/TestFramework/Assertions/Assert.Contains.cs:241

• Same issue in the non-generic predicate overload: when predicateExpression is empty, it reports the non-predicate ContainsSingle count-based failure even though actualCount represents predicate matches. This can yield incorrect/misleading failure summaries on compilers that don't supply CallerArgumentExpression. Prefer reporting the predicate-specific structured message and relying on placeholders for missing expressions; reserve the count-based message for the true collection-only overload.

        if (string.IsNullOrEmpty(predicateExpression))
        {
            ReportAssertContainsSingleFailed(matchCount, message, collectionExpression);
        }

• Files reviewed: 20/20 changed files
• Comments generated: 1

[Evangelink]

Review: PR #8265 — RFC 012 structured messages for Assert.Contains family

Good migration work. One minor duplication to fix; everything else is clean.

---

Verdict Table

#	Dimension	Status	Notes
1	Correctness	✅ LGTM	All report helpers are [DoesNotReturn]; logic is correct
2	Null safety	✅ LGTM	CheckParameterNotNull guards kept; comparer is object? by design (only .GetType().Name used)
3	Error messages	✅ LGTM	Summary strings are clear and consistent with RFC 012 pattern
4	API compat	✅ LGTM	All new methods are private static; no PublicAPI.Unshipped.txt changes needed
5	Performance	✅ LGTM	Allocations are failure-path only
6	Cross-TFM	✅ LGTM	IndexOf(char) used correctly; netstandard2.0/net462 safe
7	No init accessors on new public API	✅ LGTM	No new public API introduced
8	[DoesNotReturn] annotation	✅ LGTM	All Report* helpers carry the attribute
9	Localization / .resx	✅ LGTM	All 9 new *FailedSummary entries present in .resx
10	XLF files	✅ LGTM	Generated via UpdateXlf build target (not hand-edited); all 13 locales have state="new"
11	Test coverage	✅ LGTM	Unit tests updated for new wildcard format; ScopeTests updated with exact structured output
12	Code duplication	⚠️ MINOR	ContainsLineBreak duplicates IsMultiline from Assert.cs — same partial class — see inline comment
13	Pre-existing: DoesNotContain object loop	i️ NOTE	foreach loops (lines 536, 589) don't break after calling the [DoesNotReturn] helper, so inside an AssertScope duplicate errors are recorded for each matching element. This is pre-existing, not introduced here, but the refactor would have been a good time to add a return/break.
14–21	All other dimensions	✅ LGTM	Style, naming, nameof, pattern matching, file endings, SA1028 — all clean

---

One actionable item: The ContainsLineBreak private helper introduced in Assert.Contains.cs is identical to the existing IsMultiline in Assert.cs (same partial class). See inline comment.

Generated by Expert Code Review (on open) for issue #8265 · ● 16.9M

[Evangelink]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved in 7146652. There were two conflicting files:

• Assert.cs: Our PR had removed BuildUserMessageForSubstringExpressionAndValueExpression (no longer called after the Contains migration) and briefly added 4 suffix/prefix helpers. Since main's StartsWith/EndsWith PR (Apply structured assertion messages (RFC 012) to Assert.StartsWith / EndsWith #8258) already uses structured messages directly and never calls those helpers, they were dead code — I removed them entirely, eliminating the conflict and the IDE0051 warnings.

• FrameworkMessages.resx: Kept all 9 new entries from our PR (ContainsSingle/Contains/DoesNotContain/IsInRange *FailedSummary) alongside the 4 entries from main's Apply structured assertion messages (RFC 012) to Assert.StartsWith / EndsWith #8258 (StartsWithFailedSummary, DoesNotStartWithFailedSummary, EndsWithFailedSummary, DoesNotEndWithFailedSummary). XLF files regenerated via UpdateXlf. Build is clean: 0 errors, 0 warnings.

[Evangelink]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved in c731573. New commits on main (IComparable RFC 012, #8260) caused two more conflicts in the same files:

• Assert.cs: All conflicting helpers on both sides were dead code (our PR had already migrated IsInRange away from BuildUserMessageForLowerBound/UpperBound; main's Apply structured assertion messages (RFC 012) to Assert.IComparable family #8260 had migrated IComparable away from the collection/predicate/three-expression helpers). All dropped.

• FrameworkMessages.resx: Kept all 15 entries — 9 from our PR (ContainsSingle/Contains/DoesNotContain/IsInRange) plus 6 from main's Apply structured assertion messages (RFC 012) to Assert.IComparable family #8260 (IsGreaterThan/IsGreaterThanOrEqualTo/IsLessThan/IsLessThanOrEqualTo/IsPositive/IsNegative). XLF regenerated. Build: 0 errors, 0 warnings.