How to Discover a Bug Using Git Bisect

In the process of working on long-term projects with Git, it’s not uncommon to encounter regression bugs caused by unrelated changes in the code. To solve this problem, it is important to determine where the bug is and identify which commit introduced the issue. Git provides a useful command called bisect to automate this process and make bug discovery easier.

To begin, you can manually check out specific commits to narrow down the problematic code. This can be done using the command line or Git clients that support single commit checkout. For example, with GitHub Desktop, you can use the command git checkout <COMMIT_SHA> to roll back to a specific commit.

Once you have identified a commit where the code works correctly, you can apply the divide and conquer principle. Pick a commit between the last known working commit and the one that does not work, and repeat the process by checking out the middle commit. By cutting the interval of commits in half at each iteration, you can narrow down the commit that introduced the bug.

However, Git’s bisect command automates this process and makes it more efficient. Start by checking out the latest commit using git checkout your-branch-name, such as git checkout master. Then, run git bisect start to initialize the bisect process.

Next, specify a bad commit - a commit where the code does not work - using git bisect bad HEAD. You also need to specify a good commit - a commit where the code worked previously - using git bisect good <COMMIT_SHA>.

Git will then start the bisect process and inform you of how many revisions are left to test. It will guide you on the steps to take, indicating which commits to test next.

After testing each commit, you need to provide feedback to Git using git bisect bad if the code does not work, or git bisect good if the code is working as expected. Repeat this process until Git identifies the bad commit that introduced the bug.

Once the problematic commit is identified, you can run git bisect reset to return to the latest commit in your branch.

By utilizing the bisect command, you can make the process of bug discovery and regression testing more efficient and automated.

Tags: bug discovery, Git bisect, regression bug, version control system