Even better, if your testing framework supports it, mark the test as expecting failure in your regression commit, then remove the xfail in the commit that fixes the bug.

I actually prefer to add a passing test asserting the bug exists in one commit, then fix the bug and reverse the sense of the test in a second commit. The second commit is now more or less self documenting -- this case used to produce this buggy behavior but now produces correct behavior -- and the fact that the test originally passed provides proof that the test is capable of detecting a regression.

Put the failing test into the codebase with an `@Ignore`, have the second commit remove the `@Ignore`