java.lang.ExceptionInitializerError when using Mockito on Android

So you’re being a good Android developer, using JUnit 3 tests [Sidenote: JUnit 4 does not play well with the JUnit runner in Eclipse for Android currently] and using Mockito to create mocks to make sure you’re focusing on the class that you’re testing. However, you run into a java.lang.ExceptionInitializerError when running your tests. This is pictured below. What should you do?

tl;dr –

To use Mockito on a device or emulator, you’ll need to add three .jar files to your test project’s libs directory: mockito-all-1.9.5.jar, dexmaker-1.0.jar, and dexmaker-mockito-1.0.jar.

“Mockito on Android” from the Square Engineering Blog

Put those 3 JARs linked above in a “libs” directory in your test project.

The root cause of this is that the classes that Mockito makes needs to interact with dex, which is what Android uses to create its classes. This can be done with Dexmaker and the Dexmaker/Mockito integration. Once you add in those 3 JARs into your libs directory, just do the refresh/clean project dance and then you should be good to go.

Special thanks to Jesse Wilson (@jessewilson) for making DexMaker and integrating Mockito with Android!