Testing

Runs the code: unit and integration tests, browser tests, property-based tests, fuzzing, mutation testing.

When: On every change that alters behaviour. Add generated inputs (property tests, fuzzing) when the code parses, transforms or computes, and mutation testing when the tests themselves change.

80% of scanned repositories run at least one

17 tools detected

Unit and integration tests

called for by: any change; public apis, signatures, error paths, nullability; service and framework code; network calls, retries, timeouts, protocols; databases, migrations, caching; model, prompt and llm code

Catches: Behaviour regressions on the paths the tests exercise.

Tool	Languages	Repos	Command seen	Docs
`vitest`	javascript, typescript	91	`vitest run`	docs
`pytest`	python	77	`pytest`	docs
`cargo-test`	rust	44	`cargo test --locked`	docs
`jest`	javascript, typescript	38	`jest`	docs
`node-test`	javascript, typescript	35	`node --test`	docs
`go-test`	go	29	`go test ./...`	docs
`unittest`	python	20	`unittest`	docs
`mocha`	javascript, typescript	10	`mocha -- $npm_package_config_test_args`	docs

End-to-end browser tests

called for by: ui components and pages

Catches: User flows broken across components, routing and the network.

Tool	Languages	Repos	Command seen	Fix	Docs
`playwright`	javascript, typescript	55	`playwright test`		docs

Property-based tests

called for by: public apis, signatures, error paths, nullability; algorithms, parsers, data transforms; threads, async code, locks, shared state

Catches: Edge-case inputs nobody wrote a test for; invariants over generated data.

Tool	Languages	Repos	Docs
`proptest`	rust	11	docs
`hypothesis`	python	10	docs
`fast-check`	javascript, typescript	3	docs

Fuzzing

called for by: algorithms, parsers, data transforms; network calls, retries, timeouts, protocols

Catches: Crashes, panics and hangs on malformed input, especially in parsers and decoders.

Tool	Languages	Repos	Command seen	Fix	Docs
`cargo-fuzz`	rust	6	`cargo fuzz build -s none`		docs

Mutation testing

called for by: algorithms, parsers, data transforms; the tests themselves

Catches: Tests that keep passing whatever the code does.

Tool	Languages	Repos	Command seen	Fix	Docs
`stryker`	javascript, typescript	3	`stryker run`		docs
`mutmut`	python	1	`mutmut run 2>&1`		docs

Version and platform matrix

called for by: service and framework code; databases, migrations, caching; dependencies and lockfiles; the tests themselves

Catches: Breakage on a runtime version, OS or feature combination you did not run locally.

Tool	Languages	Repos	Command seen	Fix	Docs
`ci-matrix`	any	115	`analyze (language: 1)`		docs
`cargo-hack`	rust	4	`cargo hack check --all --feature-powerset --exclude-features $EXPR ...`		docs