Increasing test coverage with regression tests

Automated test suites don't tell you everything works - they tell you what you've tested isn't broken.

Having tests doesn't mean your code is bug-free. There could be edge cases or scenarios you haven't tested for that contain bugs, even though your test suite is passing.

What do we do?

When you find a bug, try replicating it within an automated test before attempting to fix it.

Once you have a failing test and can replicate the issue, go ahead and fix it.

If the test passes, you know you've fixed the bug and solved the issue.

Here's the thing

Now you have this test, you cannot re-add the bug again without the test failing. You've prevented anyone from accidentally re-introducing it in the future and increased your test coverage.