Bisect for finding bug-introducing commits in Git - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Bisect Start and Marking Commits

You start a git bisect session with git bisect start. You mark commit abc123 as bad and commit def456 as good. What is the next step git expects you to do?

A Manually check out the next commit git selects and mark it as good or bad

B Reset the bisect session with <code>git bisect reset</code>

C Merge the good commit into the bad commit branch

D Run <code>git bisect run</code> immediately to automate testing

💡 Hint

Think about how git bisect narrows down the commit range step by step.

After marking the known good and bad commits, git bisect checks out a commit in the middle. You must test it and mark it as good or bad manually. This helps git narrow down the commit that introduced the bug.

💻 Command Output

intermediate

Bisect Command Output Interpretation

You run git bisect bad after testing a commit. Git outputs:

Bisecting: 3 revisions left to test after this (roughly 2 steps)
Next commit to test is 789abcde

What does this output mean?

A Git encountered an error and cannot continue bisecting

B Git found the bad commit at 789abcde and bisect is finished

C There are 3 commits left to check, and git will take about 2 more steps to find the bad commit

D You must reset bisect because the range is invalid

💡 Hint

Look at the number of revisions left and the next commit hash.

The output shows how many commits remain to test and which commit git will check out next. It helps you understand progress.

❓ Troubleshoot

advanced

Bisect Session Stuck on a Commit

During a bisect session, you test a commit but the build fails and you cannot determine if it is good or bad. What is the best way to proceed?

A Skip the commit using <code>git bisect skip</code> and continue

B Mark the commit as bad to continue bisecting

C Mark the commit as good to continue bisecting

D Abort the bisect session with <code>git bisect reset</code>

💡 Hint

Think about how to handle commits that cannot be tested.

If you cannot test a commit, skipping it allows git to ignore it and continue bisecting with other commits.

🧠 Conceptual

advanced

Understanding Bisect Algorithm Efficiency

Git bisect uses a binary search algorithm to find the bad commit. If you have 128 commits between good and bad, what is the maximum number of steps git bisect will take to find the bad commit?

A 128 steps

B 7 steps

C 64 steps

D 256 steps

💡 Hint

Binary search halves the search space each step.

Binary search cuts the number of commits to check in half each step. For 128 commits, log2(128) = 7 steps max.

✅ Best Practice

expert

Automating Bisect with a Test Script

You want to automate git bisect using git bisect run with a test script that exits 0 if the commit is good and 1 if bad. Which of the following scripts is correct for this purpose?

A

#!/bin/sh
make test; exit 0

B

#!/bin/sh
exit 0

C

#!/bin/sh
if make test; then exit 1; else exit 0; fi

D

#!/bin/sh
make test && exit 0 || exit 1

💡 Hint

The script must exit 0 for good commits and non-zero for bad commits.

The script runs tests and exits 0 if tests pass (good commit), or exits 1 if tests fail (bad commit). This matches git bisect run expectations.