Scripts usable with Git bisect - the best way to find where a regression was introduced in your project.
Customize the template for your project.
See this expanded working example for a test script used in an actual case, sinonjs/sinon#1526. There are many more examples.
$ cp full-template.sh ../my-test-script.sh
$ vim ../my-test-script.sh
$ ../my-test-script.sh
Test FAIL
$ git bisect bad master
$ git checkout v2.0.0
$ ../my-test-script.sh
Test OK
$ git bisect good
$ git bisect run ../my-test-script.sh