Fast pre-commit tests

pre-commit allows you to run linting & unit tests in a pre commit hook.

Generally a pre-commit hook should only test & lint that which has changed.

Linting what has changed.

This one is easy.

jshint --verbose $(git diff --cached --name-only | grep '\\.js$')

To be able to test what has changed we need a command called node-parents

node-parents $(git diff --cached --name-only | grep '\\.js$') \
  | grep 'test' \
  | grep -v 'node_modules' \
  | xargs -L node

node-parents will take a list of files and print all the parents & grandparents & etc that require it recursively.

This allows you to find test/foo.js that requires the changed file directly or indirectly

For node-parents to be useful in this context it should have an mtime based stat cache.