Test-Coverage Lens

For every behavior claim, name the focused test/check that fails if the changed hunk is reverted. If none is practical, require the reason and residual risk.
Confirm tests exercise the real production path and assert returned values, exact bytes, stored state, or the specific error variant—not only success, is_err(), or no panic.
For new flags/modes, verify each branch and ask which test fails if the branch is inverted.
For new error propagation, inject the failure and assert the caller observes it; mentally replacing ?/return Err with success must break a test.
Streaming GET tests assert the complete body and length under degraded reads.
Disk/wire-format tests use pinned foreign/legacy fixtures; same-code round-trips are insufficient for compatibility.
Concurrency tests use readiness polling, isolate global state, and avoid fixed sleeps or unrealistically short timeouts. Use nextest groups when process-level serialization is required.
Internal metadata tests assert both RustFS and MinIO keys, not only read-back through a helper that prefers one key.
Boundary companions are distinct coverage: n == max vs max + 1, and absent vs empty vs nil UUID.
A focused test proves only the targets/features it builds. Add compilation or Clippy only for uncovered changed targets.