[samtrion]

Problem

Mutation report for Usage/RequireCancellationTokenParameterCodeFixProvider.cs, lines 236-312 (EnsureSystemThreadingUsing, InsertAlphabetically, RemoveLeadingBlankLines): 11 NoCoverage and 13 Survived mutants (29 Killed, 23 Survived, 11 NoCoverage in the file, excluding CompileError and Ignored). The tests NoParameters_AppendsTokenAndAddsUsing, FileScopedNamespace_UsingInsertedAtNamespaceLevel and BlockScopedNamespaceWithExistingUsings_UsingInsertedAtNamespaceLevel claim to test using insertion.

Root cause

All three tests have using System.Threading; already in their input, so the fix returns at if (hasUsing) return root and never runs the insertion code. The only real insertion tests reach just the append-at-end branch.

Change

• Remove using System.Threading; from the input of the three tests and fully qualify System.Threading.CancellationToken in the helper (input and expected output). The using is now inserted at compilation-unit, file-scoped and block-scoped namespace level, before an existing using System.Threading.Tasks; (insert-before branch, leading-blank-line removal).
• Add BlockScopedNamespaceNewUsingSortsAfterAllExisting_AppendedWithIndentation: the new using sorts last inside an indented block namespace, covering the append branch that copies the first using's leading trivia.

Test-only change; no product code touched.

Before / After

Measured with the mutation workflow dispatched on this branch: https://github.com/dailydevops/analyzer/actions/runs/40815375432 (before: latest successful run on main, 2026-10-27). The per-file score is not printed in the log, so the comparison is on whole-run totals.

metric	before	after
mutation score	59.95 %	60.63 %
mutants created	2110	2110
compile errors	474	474
NoCoverage	42	33
Ignored (block already covered)	n/a in summary	300
Killed	793	801
Survived	491	491
Timeout	5	6
duration	25:15	24:23

Result: 9 NoCoverage mutants are now covered and 8 more are killed, but the Survived count did not change. The gain (+0.68 points) is below the estimated 1.0-1.4 points; the 13 survivors in lines 236-301 (trailing-trivia fallback, existingUsing logic) are not affected by these tests.

Risk / what this does not change

No product code changes. Not addressed: line 270 (dead ternary, Usings.Count is always 0 there, equivalent mutants) and lines 246-247 (CRLF versus LF trailing trivia fallback, would need brittle CRLF input). Realistic expectation is roughly 14-19 fewer survivors/NoCoverage, not the full 24.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.54%. Comparing base (8c86c2b) to head (bf60594).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #230      +/-   ##
==========================================
+ Coverage   94.72%   95.54%   +0.82%     
==========================================
  Files          48       48              
  Lines        2557     2557              
  Branches      449      449              
==========================================
+ Hits         2422     2443      +21     
+ Misses         58       41      -17     
+ Partials       77       73       -4     

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