Writing unittests for AEM (part 4): OSGI services mock services

In the last parts of this small series (part 1, part 2, part 3) I covered some basic approaches how you can use the Sling and AEM mocking libraries to ease writing unittests. The examples were quite basic and focussed, but in reality many test cases turn out to be much more complex.

And especially when your code has dependencies to other OSGI services, tests can get tricky. So today I want to walk you through some unittest I wrote some time ago, it’s a unittest for the EnsureOakIndex functionality (EnsureOakIndexJobHandlerTest).

The interesting part is that the required EnsureOakIndex service references 4 other services in total; if they are not present, my EnsureOakIndex service will never start properly. Thus you have to fullfill all service requirements of an OSGI service in the unittest as well (at least if you want to use SlingContext like I do here).

The easiest way to solve this is to rely on predefined services which are part of the SlingMocks or AemMocks. The second best way is to create simple mocks and register them a service, so the dependency is fulfilled. That’s definitely a convenient way if your tests do not invoke any of the service methods at all.

Thus the setup() method of my unittests are often pretty large, because there I prepare and inject all other services which I need to make my software-under-test work.

And because this setup works quite well and reliably, I always use AemContext for my unittests (or SlingContext, but as I haven not yet observed any difference in test execution time, I often prefer just AemContext because it comes with some more sevices). Just if I don’t need resources, nodes and no OSGI, I stick with plain junit. For everything else AemContext removes the necessity for mocking a lot.

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