Although Drupal SimpleTest is an extremely useful module it doesn't currently support data providers, which is a shame as I use that feature quite a bit in other testing frameworks. A data provider is a mechanism that allows you to call a single test case multiple times with different arguments so that you can ensure the correct output each time. This is useful because testing a single function once is fine, but testing it with a variety of different values can otherwise mean having multiple test cases.
To mimic this functionality in Drupal SimpleTest you can create a data provider method that returns an array, which is then used to test a particular function.
For example, let's say I have the following (trivial) function in a Drupal module.