Testing Assertion Author

Use this skill when the user asks to:

• write tests
• improve assertions/diagnostics
• create fixtures/golden files
• structure table tests
• refactor brittle tests into stable patterns

Mandatory references (read in order)

1. references/testing.md
2. references/nonnegotiables.md (still applies: no ignored errors, no compound init if)
3. references/testutil.md
4. references/jsontest.md
5. references/fsfix.md
6. references/pipefunc.md