[samtrion]

Problem

The latest mutation run on main reports about 11 survivors on guard clauses that are not part of the failing-test cluster (per the report; the log only carries totals: 51 survived, 40 of them only covered by failing tests). Affected spots:

• ProjectBuilderExtensions.AddVBFile: ThrowIfNullOrWhiteSpace(fileName) and (content)
• ProjectFactoryExtensions.AddGlobalJson: ThrowIfNullOrWhiteSpace(runtimeVersion) and configure?.Invoke(builder)
• GlobalJsonBuilder.SetRuntimeSdk whitespace guard and CreateAsync ThrowIfCancellationRequested
• Duplicate-file message strings in SubdirectoryBuilder.CreateFile and TemporaryDirectoryBuilder.CreateFile (message mutated to empty)

Root cause

Empty-name and empty-content tests exist only for AddCSharpFile. AddGlobalJson has no unit test (only integration tests, which fail in the CI container). The duplicate-file tests assert only the exception type, not the message.

Change

Test-only. New unit tests:

• AddVBFile with empty/whitespace file name and content
• AddGlobalJson with empty/whitespace runtime version, and the configure callback (invoked once, receives a GlobalJsonBuilder) in a new ProjectFactoryExtensionsTests
• SetRuntimeSdk with empty/whitespace
• GlobalJsonBuilder.CreateAsync with a pre-cancelled token (may turn out equivalent for mutation purposes)
• Duplicate-file tests now assert the message contains the file name and "already exists"

Unit suite passes locally (378 tests, net10.0).

Before / After

Run: https://github.com/dailydevops/projectbuilders/actions/runs/40810654395 (mutation.yml dispatched on this branch) vs. the latest main run.

metric	before	after
mutation score	74.73 %	76.23 %
killed	349	356
survived	51	44
survived (only covered by failing tests)	40	40
compile errors / no coverage / ignored	27 / 27 / 109	27 / 27 / 109
failing tests in initial run	16 / 14 / 30	16 / 14 / 30
runtime	9 min	13.5 min (runner variance, test count increased only slightly)

Seven mutants were killed, at the low end of the approximately 8 to 11 estimate. The remaining survivors outside the failing-test cluster are not itemised in the log, so which ones remain is not verified.

Risk / what this does not change

No production code change. The failing-test cluster (integration tests failing in the container) is untouched and still limits the achievable score.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.69%. Comparing base (3375b9a) to head (46fe69c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #262   +/-   ##
=======================================
  Coverage   89.69%   89.69%           
=======================================
  Files          31       31           
  Lines         728      728           
  Branches       85       85           
=======================================
  Hits          653      653           
  Misses         67       67           
  Partials        8        8           

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