tests are very important, often 1 test is equivalent to 20 future bug fixes. documentation gets outdated, comments get outdated, but tests never get outdated. they document the behaviour and enforce it on each change.
countless times it has happened that i pushed some code and someone broke it. qa tagged me on that because they found my commit introduced the now-buggy-feature. having tests ensures this never happens, when you push a test, you are saying "don't break my code!".