My attitude with tests is not to write individual tests when I can write property-based tests. The payoff from the latter is considerable. Let the computer do the work of generating and running tests; its time is worth a whole lot less than mine.

For individual tests, say for coverage, these should also be generated automatically if possible, say by looking for inputs that kill mutants. I've backburned a Common Lisp system for doing this, generating mutants from Common Lisp source forms and automatically searching for and minimizing inputs that kill new mutants. Maybe one day I'll finish this and put it out there for general use.