[Brooooooklyn]

Requested by Brooklyn · project thread

Before: five unit tests could not fail on a regression that no other test catches: a f() == f() tautology, a "hash twice and compare" check, and three tests whose assertions are a subset of a neighbour's. Two fspy_shared_unix tables and the labeled-writer tests were hand-unrolled into one #[test] per row.

After: the five tests are gone, and the three tables are table-driven tests that keep every row, its inputs and its expected value. Only #[cfg(test)] code changes.

How: each removal was defended by mutating product code with the most realistic regression it could catch, running the crate's tests, and reverting.

Totals

• Files touched: 8, test modules only.
• Cases deleted: 5. Cases merged: 18 rows folded into 3 table-driven tests (21 tests become 3). Across the six crates run (fspy_shared_unix, vt, vt_glob, vt_powershell, vt_workspace, vt_plan lib tests): 282 → 259 cases. The whole workspace was not run (see below), so there is no workspace-wide total.
• Net lines: −169 (+107 / −276).
• Runtime saved: about 34 ms, the summed duration of the deleted cases (npm_workspace_with_exclusions 28 ms, test_file_hashes_are_consistent 6 ms, the rest under 1 ms).

Removals

1. vt_powershell tests::is_stdin_terminal_is_idempotent — tautology: assert_eq!(is_stdin_terminal(), is_stdin_terminal()) on a LazyLock. Mutation R1 (negate the cached is_terminal()): the test passes, as does everything else in vt_powershell and vt_plan. The behaviour that depends on it is covered by vt_plan ps1_shim::tests::skips_rewrite_when_not_interactive (mutation R1b, skipping the !is_interactive check, fails it).
2. vt session::execute::glob::tests::test_file_hashes_are_consistent — determinism check. Mutation R2 (seed the file hasher randomly per call) fails it and also session::execute::hash::tests::other_files_hash_raw_content and redacted_file_hashes_without_content, which pin exact hash values.
3. vt session::reporter::grouped::writer::tests::buffers_output — subset of shared_buffer_interleaves, which appends several chunks from two writers to one shared buffer and checks the joined result. Mutation R5 (replace instead of append) fails both.
4. vt_glob path::tests::test_match_ignores_directory_only_patterns — build/** with !build/keep/**; test_match_ignores_directory_patterns asserts the same shapes (build/**, dist/** with !dist/public/**). Mutations R4 (ignore negations) and R4b (treat negated globs as positive) fail 8 and 9 other path tests.
5. vt_workspace tests::test_get_package_graph_npm_workspace_with_exclusions — despite its name it only asserts that the root and packages/normal are found; its closing comment says exclusions "might not work" and asserts nothing about them. Mutation R3 (drop negated workspace globs): it passed (run at the earlier base), while test_get_package_graph_workspace_exclusions, …_workspace_work_with_last_match_wins and …_npm_workspace_with_root_relative_prefixes fail. Mutation R3b (stop adding the root package) fails 13 other graph tests, test_get_package_graph_npm_workspace among them.

Folds (every row kept)

File	New test	Rows	Mutation that fails it
fspy_shared_unix/src/exec/mod.rs	appends_value_to_the_env_list	7	RF2: always prepend :
fspy_shared_unix/src/exec/which.rs	test_which	8	RF3: ENAMETOOLONG → ENOENT
vt/src/session/reporter/labeled/writer.rs	prefixes_each_line	6	RF1: drop the prefix

Each assertion carries the row's name, so a failure still names the case.

Kept after defense

• vt_subprocess_test tests::test_command_for_fn was nominated and kept: its defense could not be completed safely (see "What ran").

Case counts (lib tests)

crate	before	after	delta
fspy_shared_unix	30	17	−13 (folds)
vt	88	81	−7 (2 deleted, 5 folded)
vt_glob	23	22	−1
vt_powershell	6	5	−1
vt_workspace	85	84	−1
vt_plan	50	50	0

0 failures before and after.

What ran and what did not

• Ran on Linux at 0346c268 and on this branch: the lib tests of the six crates above with --report-time; mutations R1–R5, R1b, R3b, R4b and RF1–RF3, each reverted afterwards; cargo fmt --check on the touched files; cargo clippy -p fspy_shared_unix -p vt -p vt_glob -p vt_powershell -p vt_workspace --tests -- -D warnings (clean).
• Not run: the workspace-wide just lint and just test, macOS and Windows, and the e2e/snapshot suites. The vt_subprocess_test and vt_pty_terminal suites were deliberately not run: while defending test_command_for_fn, a mutation that swapped the child's id and payload arguments left children with an empty argument, which libtest took as a filter matching every test, so each child re-ran the suite and spawned without bound.

Open pull requests: of the 61 open, only #601 touches a file here, and it renames crates/vt/src/session/execute/glob.rs without changing its content.

Ages: all five deleted tests are older than a month (newest: is_stdin_terminal_is_idempotent, 2026-06-28). None was added for a bug, and none is in a permission or security suite.

To revert: git revert 2c324106.

---

Generated by Claude Code

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Review	Status	Commit	Review trigger
📝 Code Review	🔄 Running since 2026-10-24T19:40:54.457436Z	2c32410	PR opened

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[github-actions]

fspy benchmark

linux

dynamic/launch             change  -0.13%  [ -2.79% ..  +2.38%]  overhead   +49.76%
dynamic/access             change  -0.37%  [ -3.21% ..  +3.44%]  overhead   +18.57%
dynamic/access-relative    change  +0.89%  [ -1.74% ..  +3.15%]  overhead   +73.63%
dynamic/access-contended   change  +1.85%  [ -2.76% ..  +5.22%]  overhead   +38.27%
static/launch              change  +0.42%  [ -2.26% ..  +2.82%]  overhead  +183.99%
static/access              change  +0.06%  [ -0.69% ..  +0.73%]  overhead +1437.91%
static/access-relative     change  -0.30%  [ -1.74% ..  +0.54%]  overhead +1937.23%
static/access-contended    change  +0.07%  [ -0.77% ..  +1.07%]  overhead +2074.27%

macos

dynamic/launch             change  -0.30%  [ -4.94% ..  +4.29%]  overhead  +231.78%
dynamic/access             change  +0.00%  [-34.06% ..  +9.44%]  overhead    +5.43%
dynamic/access-relative    change  +0.00%  [ -5.62% ..  +5.96%]  overhead  +260.31%
dynamic/access-contended   change  +1.47%  [-17.70% .. +30.24%]  overhead    +5.54%

windows

dynamic/launch             change  +0.20%  [ -1.86% ..  +2.56%]  overhead   +24.65%
dynamic/access             change  +0.00%  [ -0.79% ..  +0.60%]  overhead    +1.16%
dynamic/access-relative    change  +0.00%  [ -0.58% ..  +0.95%]  overhead    +1.35%
dynamic/access-contended   change  -0.18%  [ -0.91% ..  +0.72%]  overhead    +0.95%