Keep your tests clean. Treat them as first-class citizens of the system.

Clean Coder Blog: "when people give up on unit tests, it’s usually because they haven’t followed the above author’s advice. They have not treated the tests like first-class citizens. They have not treated the tests as though they were part of the system. They have not maintained those tests to the same standards that they apply to the rest of the system. Instead, they have allowed the tests to rot, to become coupled, to become rigid, and fragile, and slow. And then, in frustration, they give up on the tests. Moral: Keep your tests clean. Treat them as first-class citizens of the system."