[chore] Test gap fills: testutil.LoadFixture panic path and e2e for rimba completion

[lugassawan]

Type

• Tests (coverage gaps, e2e, fixtures)

Files to change

• testutil/testutil_test.go
• tests/e2e/completions_test.go (new file)

Description

G4 — testutil.LoadFixture panic path untested
testutil/fixture.go:LoadFixture calls t.Fatalf when the fixture file cannot be read, but testutil/testutil_test.go only tests the happy path (fixture file exists and is readable). The failure path (non-existent file, permission error) is not exercised, which means the error message and the t.Fatalf call itself are untested. Add a subtest that calls LoadFixture with a path that does not exist and asserts that the test is marked as failed (using a testing.TB spy or t.Run with a fresh helper T).

G5 — No e2e test for rimba completion
rimba completion (shell completion generation) has no entry in tests/e2e/. Running rimba completion bash, rimba completion zsh, and rimba completion fish all produce output but are never exercised in the e2e suite. Add a tests/e2e/completions_test.go that:

1. Builds the rimba binary
2. Runs rimba completion bash (and optionally zsh, fish)
3. Asserts exit code 0 and that stdout contains known completion markers (e.g., complete for bash, compdef for zsh)

Acceptance

• testutil_test.go contains a subtest for LoadFixture with a missing file path; test marked as failed by the helper.
• tests/e2e/completions_test.go exists and passes for at least bash completion.
• make test and make test-e2e pass.
• Coverage does not drop below 97%.

Bundles

Original candidates folded into this issue:

• G4 (testutil/testutil_test.go): LoadFixture failure path (missing file → t.Fatalf) is not tested.
• G5 (tests/e2e/): no e2e coverage for rimba completion subcommand.