composer require --dev brianium/paratest
./vendor/bin/paratest --processes=4
# Run specific suites
./vendor/bin/phpunit --testsuite=Unit
./vendor/bin/paratest --testsuite=Unit --processes=8
# Speedup example:
# Sequential: 45 seconds
# Parallel (4 cores): 14 seconds
# Tests must be truly isolated — no shared state