someone will test your software
The majority of testing should be performed by development teams
manual testing should not be the majority of your testing because manual testing is O(n)
Manual testing of software or manual verification of a defect is not sufficient because it does not scale.
针对bug情况：
First response when given a bug to fix or a feature to implement should be to write a failing test. This doesn’t need to be a unit test, but it should be an automated test. Once you’ve fixed the bug, or added the feature, now have the test case to prove it worked–and you can check them in together.
Tests lock in behaviour(TDD)