jUnit: Rules

Rules add special handling around tests, test cases or test suites. They can do additional validations common for all tests in the class, concurrently run multiple test instances, set up resources before each test or test case and tear them down afterwards.

The rule gets complete control over what will done with the test method, test case or test suite it is applied to. Complete control means that the rule decides what to do before and after running it and how to deal with thrown exceptions.

jUnit: Dynamic Tests Generation

Dynamic tests generation is useful when you need to run the same set of tests on many different input values or configurations. It can be achieved either using parametrized tests or using theories.

Theories are valuable when you have a bunch of data to be used as parameters and want to run tests on all their combinations. You get less control, but you do not have to write combining and iterating code by yourself. Basics about how theories work are explained on java code geeks (original at java advent calendar), so this post focus on parametrized tests.

Parametrized tests are better when you need to have good control over the input values, e.g. directory with files that are served as an input or a list of meaningful parameters combinations.