Prove the Test Can Fail: Mutate the Fix

After you write the test that goes with your fix, revert the fix and watch the test fail. That takes about thirty seconds, and no other single habit has done as much for my confidence in a diff. &#xA; That&rsquo;s it. That&rsquo;s the whole technique. I now consider a regression test unverified until I&rsquo;ve seen it red, and I ask for the same from anything that writes code on my behalf.