Find the commit that introduced a bug with git bisect

Backend Live Coding November 13, 2026 bash

git bisect does a binary search: for 200 commits it needs about 8 steps.

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# ======================================================================
# Q: A bug appeared sometime in the last 200 commits. How do you find which one
# caused it?
#
# git bisect does a binary search: for 200 commits it needs about 8 steps. The
# key is to have a test that reproduces the bug, so I write it first (and it
# stays as a regression test). This is also one reason I want small, atomic
# commits: bisect points you to a 20-line change, not a 3,000-line commit.
# ======================================================================

git bisect start
git bisect bad HEAD              # it is broken now
git bisect good v2.14.0          # it worked at this tag

# automatic: the script returns 0 = good, 1 = bad, 125 = skip
git bisect run pytest tests/test_pricing.py::test_volume_discount -x -q

git bisect reset                 # return to the original HEAD

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