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How to test static members with Mockito in Flutter

manuelvargastapia profile image Manuel Vargas ・2 min read

I'm starting my journey with unit testing in Flutter. Early in the process, while I was writing tests for my Firebase sign in workflow, I faced a situation that I struggled to surpass and want to share. I needed it to test a static member call.

Concretely, I wanted to test a call to the GoogleAuthProvider.credential() static method. I wanted to do this to get the OAuth credentials and pass them to FirebaseAuth.signInWithCredential(). This way I could use Google Sign In through Firebase Authentication.

call to GoogleAuthProvider.credential()

In my test, I couldn't mock this static method call. All my attempts failed. My only hope was to refactor my code to make it testable for this particular case.

failed test

After several failed attempts -such as creating a mock to override the static method, doing the same with Fake instead of Mock, etc-, I realized that the solution implies wrapping the call in a class, so I'll be able to test it indirectly. However, the test structure requires this new wrapper class to be passed as a dependency for the class where the relevant call takes place.

first attempt

Well, the test will pass if I mock this new wrapper class and use it in when(). But I didn't want to depend on this class and make my overall architecture ugly and ad-hoc.

Finally, I decided to make this little modification:

little modification

This way, making the dependency optional, I could mock my wrapper class, call it on when(), and pass the test, without compromising my overall structure.

Also, this new wrapper eventually could serve as a place to implement additional forms of authentication, besides GoogleOAuthCredentials.

pass test


I'm learning a lot of unit testing with these kinds of situations and enjoying testing my apps. I hope eventually implement Widget and integration testing too for this same project.

Discussion (2)

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Coding Monkey

Hi if you don't mind how to take screenshots like that 😅.

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