Streamline Testing with Pest Test Impact Analysis (TIA)

Enable the Tia Engine in Pest to only re-run tests affected by your latest code changes while replaying cached results for unaffected tests.

Running full test suites on every minor change slows down local feedback loops. While --dirty only checks if test files themselves changed, Pest's Tia Engine analyzes code coverage mapping to identify tests that execute the actual application lines you modified.

1. CLI Usage

Run Pest with the --tia flag:

# Run tests with Test Impact Analysis enabled
./vendor/bin/pest --parallel --tia

On the initial run, Pest records a dependency graph of which tests touch which files. On subsequent runs, it only re-runs affected tests and replays cached results for the rest.

2. Configuration in tests/Pest.php

To avoid typing --tia on every run, configure the Tia Engine fluently inside tests/Pest.php:

// tests/Pest.php

pest()->tia()
    ->locally()   // Run TIA on every local invocation; skipped automatically in CI
    ->baselined() // Fetch shared baseline from CI when no local graph exists
    ->filtered(); // Narrow test runner to affected test files only
  • locally(): Recommended. Activates TIA for every local pest run without requiring the --tia flag. In CI (or with --ci), TIA is skipped automatically so pipelines run the full suite.
  • always(): Alternative to locally(). Enforces TIA across all environments including CI.
  • baselined(): Downloads the shared CI baseline artifact so developers replay immediately on fresh clones.

Key Rules & Requirements

  • Coverage Driver: Requires a code coverage driver (PCOV or Xdebug) to build the dependency graph.
  • Cosmetic Invariant: Whitespace changes, comments, and docblock edits produce identical hashes, executing zero tests.
  • CLI Overrides: Bypass or force TIA anytime using --tia or --no-tia.