Producing a test specification, including the design of test cases, is the level of test design which has the highest degree of creative input. Furthermore, unit test specifications will usually be produced by a large number of staff with a wide range of experience, not just a few experts. This paper provides a general process for developing unit test specifications and describes some specific design techniques for designing unit test cases. It serves as a tutorial for developers who are new to formal testing of software, and as a reminder of some finer points for experienced software testers.