How to check if a GitHub commit broke the app?

 
Step 1: Clone the repository
 

• Open your terminal or command prompt.
• Navigate to the directory where you want to store the project.

git clone https://github.com/your-username/your-repo.git
cd your-repo

 
Step 2: Ensure you’re on the correct branch
 

• List all branches to confirm the main branch name.
• Check out the main or development branch where you suspect the breaking commit resides.

git branch -a
git checkout main
git pull origin main

 
Step 3: Install dependencies and build the app
 

• Install project dependencies according to your stack (npm, yarn, pip, etc.).
• Build or start the app to ensure it runs before exploring commits.

# example for a Node.js app
npm install
npm run build
npm start

 
Step 4: Run your test suite manually
 

• If you have automated tests, run them locally first.
• Note any test failures or errors in the console.

# example using Jest for JavaScript
npm test

# or for Python projects
pytest

 
Step 5: Use git bisect to pinpoint the bad commit
 

• Start the bisect session, marking the current (bad) state and a known good state.
• Git will check out a commit in the middle; test your app there.

git bisect start
git bisect bad             # mark the current commit as bad
git bisect good v1.2.3     # replace v1.2.3 with a known good tag or commit

 
Step 6: Test each bisect step
 

• After each checkout, build and test the app:

npm install
npm test

• If tests fail or the app breaks, mark it bad; otherwise mark it good.

# when broken
git bisect bad

# when working
git bisect good

 
Step 7: Review the result and identify the culprit
 

• Once bisect completes, Git prints the problematic commit hash and message.
• Inspect the diff to understand what change broke your app.

# git will output something like:
# abc1234 is the first bad commit
git show abc1234

 
Step 8: Fix, revert, or patch the broken commit
 

• Decide whether to create a fix on top of the bad commit or revert it entirely.
• Implement your fix, run tests again, and commit your changes.

# to revert
git revert abc1234

# to patch manually
# edit files to fix the bug
git add .
git commit -m "Fix broken feature introduced in abc1234"

 
Step 9: End the bisect session
 

• Once you have resolved the issue, stop git bisect to return to your branch head.

git bisect reset

 
Step 10: Push your fixes and create a pull request
 

• Push your fixed or reverted changes to your remote repository.
• Open a Pull Request on GitHub, explaining what commit was broken and how you fixed it.

git push origin main
# then on GitHub, click "Compare & pull request"

 
Conclusion
 

• You’ve learned how to use git bisect alongside local testing to identify exactly which commit broke your app.
• With this workflow, you can efficiently pinpoint regressions and maintain a stable codebase.