[Chris-Wolfgang]

Makes every test assembly report coverage at 100%, so Stage 1 on the sync PR stops failing with "tests ran but no coverage was recorded".

Unblocks #313; part of #307.

Per assembly

Assembly	Cause (evidence)	Fix	Before	After
Tests.DocExamples	No coverlet.collector reference (#313's Stage 1: Coverage: none collected)	Add coverlet.collector 10.0.1 (same as Tests.Unit), then cover the gaps below	no row	100%
Tests.Fuzz	No coverlet.collector reference (same log)	Add coverlet.collector 10.0.1, then cover the gaps below	no row	100%
Tests.Unit	already collected	unchanged	100%	100%
Wolfgang.Extensions.IComparable (src)		unchanged	100%	100%

Once collected, DocExamples measured 90.1% and Fuzz 96%. The uncovered lines and what changed:

• Fuzz (IComparableExtensionsProperties.cs): the two null-receiver properties used try { call; return false; } catch (ArgumentNullException) { return true; }. return false cannot run on a passing run. They now use Assert.Throws<ArgumentNullException> (which fails the property when nothing is thrown) and return whether ParamName is value, which is a slightly stronger check than before.
• DocExamples (DocExampleRotTests.cs):
  • The failure message built its list with a lambda that only ran when an example failed to compile. It now joins the diagnostics directly (string.Join(NewLine, errors)); the message still names the example's file:line and each diagnostic.
  • FindSrcDirectory now takes its start directory (production call passes AppContext.BaseDirectory, as before), so the "src not found" throw is tested.
  • The library reference was added behind if (... && seen.Add(lib)), which was always false because the test host's TPA list already contains the library. It is now added first, unconditionally, and the TPA loop skips it as already seen.
  • DocExample's parameterless constructor and Deserialize (used by xunit when discovery and execution are split) are exercised by a serialization round-trip through xunit's real SerializationHelper.
• Tests.Unit csproj: SuppressTfmSupportBuildWarnings added. dotnet nuget why shows System.IO.Hashing 10.0.12 comes in through Microsoft.SourceLink.GitHub 10.0.401, and its buildTransitive targets warn on net5.0/6.0/7.0. This was 3 warnings in a Release build before the change and 0 after.

Exclusions removed

None. There were no [ExcludeFromCodeCoverage] attributes under tests/, and none were added.

Test changes (for review)

• Added: tests/Wolfgang.Extensions.IComparable.Tests.DocExamples/DocExampleInfrastructureTests.cs with 2 tests: FindSrcDirectory_when_no_ancestor_contains_the_src_project_throws_DirectoryNotFoundException and DocExample_when_round_tripped_through_xunit_serialization_preserves_every_property.
• Changed: DocExampleRotTests.cs (failure-message lambda, FindSrcDirectory(string), library-reference ordering).
• Changed: IComparableExtensionsProperties.cs (two null-receiver properties, as described above).
• csproj: DocExamples and Fuzz add coverlet.collector; Unit adds SuppressTfmSupportBuildWarnings.

Verified locally (Windows, this branch)

• dotnet build IComparable-Extensions.slnx -c Release: 0 warnings, 0 errors.
• dotnet test on the slnx: all green. Unit had 117 tests on each of net5.0 through net10.0 and 111 on net462/472/48/481. Fuzz had 12 and DocExamples 5, both on net10.0.
• Reproduced Stage 1 as the sync branch runs it: each test project on its net5.0–net10.0 TFMs with --collect:"XPlat Code Coverage" --settings coverlet.runsettings, then dotnet reportgenerator. Summary.txt has a row for every test assembly that ran (DocExamples, Fuzz, Unit; AotSmoke is not a test project and is skipped there too). Every row is at 100%, and src is at 100%.

No changelog fragment: nothing under src/ changed.

Round 2 (2026-10-04)

Re-measured with #313's Round 2 config (repo-template#701 Stage 2 integration skip, and #702 coverlet.runsettings with comma-separated lists and <Exclude> limited to [*]AutoGeneratedProgram). Local run: this PR's head a1aa6ef, Release, net8.0 + net10.0. Every assembly stays at 100%: src, Tests.DocExamples, Tests.Fuzz and Tests.Unit, under both the old and the new runsettings. No further test changes were needed.

Merge order: this PR first, then #313.

🤖 Generated with Claude Code

[Copilot]

Copilot review overview

🟢 Approval recommended

The changes correctly close the stated coverage gaps without altering production behavior.

Review effort: Balanced
Findings: None

What changed in this PR

Ensures all test assemblies participate in the repository’s 100% coverage gate.

Changes:

• Adds Coverlet collection to DocExamples and Fuzz tests.
• Covers previously unreachable infrastructure paths.
• Suppresses known legacy-TFM dependency warnings.

File	Description
tests/​Wolfgang.Extensions.IComparable.Tests.Unit/​Wolfgang.Extensions.IComparable.Tests.Unit.csproj	Suppresses known TFM support warnings.
tests/​Wolfgang.Extensions.IComparable.Tests.Fuzz/​Wolfgang.Extensions.IComparable.Tests.Fuzz.csproj	Enables coverage collection.
tests/​Wolfgang.Extensions.IComparable.Tests.Fuzz/​IComparableExtensionsProperties.cs	Strengthens null-receiver properties.
tests/​Wolfgang.Extensions.IComparable.Tests.DocExamples/​Wolfgang.Extensions.IComparable.Tests.DocExamples.csproj	Enables coverage collection.
tests/​Wolfgang.Extensions.IComparable.Tests.DocExamples/​DocExampleRotTests.cs	Makes harness paths testable and reliably references the library.
tests/​Wolfgang.Extensions.IComparable.Tests.DocExamples/​DocExampleInfrastructureTests.cs	Tests source lookup failure and serialization.

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