Today (err, recently) I learned … that JUnit’s extension API allows for parameter resolvers. These kick in every time you use arguments on a test method, lifecycle method or class constructor. For me, so far, none of these methods ever took an argument. But turns out, it’s possible … and even useful.
They have a primitive example here where they allow a test method to take a random number like so:
@Test
void shouldDoStuff(@Random int number) {
// actually do stuff here ...
}
… in essence you just need an annotation interface, that’s linked to an extension class, that implements ParameterResolver interface (which just has two methods to implement).
My Use-case
Recently I’ve been spending my spare time on a tool called cadiff, which is about diff-ing bpmn diagram files. Literally all of the integration tests need to load two bpmn files, parse them and then actually start testing/asserting stuff. This easily starts to bloat your tests.
Enter Parameter Resolvers, my tests now look like this (at least the setup code):
@Nested
public class WithRef extends AbstractComparePatchIT {
public WithRef(@BpmnFile("empty-diagram.bpmn") final BpmnModelInstance from,
@BpmnFile("error-end-event-with-ref.bpmn") final BpmnModelInstance to) {
super(from, to);
}
// actual tests ...
}