Test suites in Android SDK are not consistent and since all modules belong to the same project and team, they should be. The issue is that in core there is no presence of mocks and dummy clases are used instead, whereas in auth Mockito is used for the same cases.

DISCLAIMER: it is OK to use both dummy classes and mocks at the same time, but not for the same exact purposes like emulating a ServiceConfiguration:

Auth: https://github.com/aerogear/aerogear-android-sdk/blob/master/auth/src/test/java/org/aerogear/mobile/auth/authenticator/OIDCAuthenticatorImplTest.java#L181-L184

Core: https://github.com/aerogear/aerogear-android-sdk/blob/master/core/src/test/java/org/aerogear/mobile/core/metrics/MetricsServiceTest.java#L44-L45