test-impact

test-impact is a Node CLI that finds changed files in git, builds a project dependency graph, and runs only impacted tests.

Why this matters

Large TypeScript repos can spend most CI time running unaffected tests. test-impact narrows test execution to only files impacted by dependency changes.

How it works

1. Read changed files from git diff --name-only HEAD (or --base=<branch>).
2. Scan project .ts and .js files.
3. Parse imports with lightweight regex parser.
4. Build directed dependency graph and reverse graph.
5. Traverse reverse graph from changed files.
6. Select reachable test files (.test.ts / .spec.ts).
7. Print impacted tests and run vitest unless --dry-run.

Installation

npm install -D test-impact

Usage

npx test-impact --dry-run
npx test-impact --base=main
npx test-impact --base=origin/main --verbose

Example output

Impacted test files:
  - src/service/user.test.ts
  - src/service/auth.spec.ts

Summary: 2 impacted test(s)

Example repo demo

Fixture repo and tests are under test/fixtures/repo.

npm test

Performance comparison (illustrative)

| Mode | Tests executed | Runtime | | --- | --- | --- | | Full suite | 1,200 | 4m 40s | | test-impact | 86 | 31s |

v2 roadmap

• Watch mode
• Graph caching
• Jest runner integration
• TypeScript Compiler API import parsing