Only write what you need.

I don't recall where I read this, but someone once wrote that each line of code should be viewed as a liability.

At work, a colleague and I have begun referring to the test code as a contract; it describes the behavior of the system. The more tests, the tighter the contract. By extension, the more code in the system, the more restrictive the implicit contract. The implicit contract is the written, and all to often unwritten, expectations of the system.

So the less code needed to get the job done, the better.