test_fakes.java

// This is the fake we create
Database fakeDatabase = new Database() {
  Map<Long, ApplicationKey> applications = Maps.newHashMap(
      APP_ID, new ApplicationKey(APP_ID, Status.REVOKED)
  );
  
  @Override
  public ApplicationKey getApplicationKey(Long id) {
    return applications.get(id);
  }
}

// Class that we want to test and that uses fakeDatabase
ApplicationService service = new ApplicationService(fakeDatabase);

// Test ApplicationService behaviour
assertThat(service.isRevoked(APP_ID), is(true));