dig the trenches before the bombs start falling

If I write code without tests I will end up with low quality code. Worse - I'll discover that having written code without tests I've naturally ended up with a codebase that resists being tested. When this happens the codebase is not being 'malicious'. That's just that way it is. That's exactly the way I grew it. Testability isn't something that appears by magic. If I want a codebase to be testable I have to write tests for it as I go along. So that I find out just how testable it actually is and steer accordingly.

Sun Tzu put it very well in The Art of War when he wrote:

Plan for what is difficult while it is easy, do what is great while it is small.