Git Bisect

Code

#!/bin/bash

# Start binary search
git bisect start

# Mark current (broken) version as bad
git bisect bad

# Mark known good version as good
git bisect good v1.0.0
# Or
git bisect good <commit-hash>

# Git auto-checks out middle commit
# Mark after testing
git bisect good  # No issue
git bisect bad   # Has issue

# Repeat until problem commit found
# Git shows: <hash> is the first bad commit

# End binary search
git bisect reset

# Automated bisect
# Write test script test.sh
cat > test.sh << 'EOF'
#!/bin/bash
npm test
exit $?  # 0=good, 1-125=bad, 125=skip
EOF
chmod +x test.sh

git bisect start HEAD v1.0.0
git bisect run ./test.sh
# Git auto-tests each commit, finds issue

# Skip untestable commits
git bisect skip

# View progress
git bisect log

# Revert to previous state
git bisect visualize
git bisect view

# Scenario: locate bug-introducing commit
git bisect start
git bisect bad              # Current version has bug
git bisect good v2.0.0     # v2.0.0 is good
# Git checkout middle commit
# Run tests...
git bisect bad              # This commit has bug
# Continue bisecting...
# Finally found first bad commit

Explanation

git bisect quickly locates commits that introduced issues via binary search; it can be automated with test scripts.

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