How many unit tests should I write per function/method?

Question

Do you write one test per function/method, with multiple checks in the test, or a test for each check?

Answer 1

I have a test per capability the function is offering. Each test may have several assertions, however. The name of the testcase indicates the capability being tested.

Generally, for one function, I have several "sunny day" tests and one or a few "rainy day" scenario, depending of its complexity.