Git bisect Demo

This repository demonstrates how to use git bisect. When you check out master, the tests in test1.js fail. When did this bug get introduced?

Installation

Clone the repository and install the dependencies.

git clone https://github.com/fhinkel/git-bisect-demo.git
npm install

npm test passes, but npx mocha test1.js fails. We forgot to add these tests to the test script. At some point in the past, the tests were all passing. When did the bug get introduced?

Let's use git bisect to find out.

How to use git bisect

git bisect start
npx mocha test1.js #  Double check that head is broken.
git bisect bad
git log --oneline # Let's find the hash for a good commit.
git checkout b58217f #  This is the first good commit.
npx mocha test1.js # Double check that everything was green.
git bisect good

Follow the interactive prompt. At every step, run the tests with npx mocha test*.js and mark the commit as either good or bad.

If you can't run the tests in a meaningful way for a specific revision, you can skip that revision.

When you've found the wrong commit, inspect the changes. Can you see what went wrong? Note the hash of the broken commit. Then call git bisect reset to exit bisection mode.

Fix the problem, either manually or by reverting the commit that broke it. Also fix the test script in package.json. It should include test1.js so we chatch bugs in the future.

You're all done. Great job!

Automating git bisect

Instead of manually running git bisect, you can automate the process. Simply pass a command to git bisect run and let git do the rest.

git bisect run npx mocha test1.js

Contributing

Pull requests and issues welcome.