Wraps LaunchDarkly server-side SDK testing patterns: TestData data source for hermetic tests (no network), file-based data source for fixture-driven tests, flag override patterns (TestData.update for per-test flag values), and assignment-integrity tests. Use when writing tests for code that uses LaunchDarkly flags; to decide which flag combinations those tests should cover in the first place, see feature-flag-test-matrix-reference.