The rise of component-based software development has created a need for API documentation. Experience has shown that it is hard to create and maintain precise and readable documentation. Prose documentation can provide a good overview but lacks precision.
Formal methods offer precision but the resulting documentation is expensive to write and modify.
Worse, few developers have the skill or inclination to read formal documentation. We present a pragmatic solution to the problem of API documentation. We augment the current prose documentation with test cases, including expected outputs, and use the prose plus the test cases as the documentation. Typically, there are one or two simple test cases for each likely question about API behavior. With this approach, the documentation is precise, albeit partial.