### Question:
StatefulPreferencesUsageService implements UsageService { @Override public long getTotalUsage() { return dataStore.getTotalUsage(); } @Inject  StatefulPreferencesUsageService(List<Module> modules, PreferencesUsageDataStore dataStore); @Override void incrementUsageFor(String moduleId); @Override List<Module> getMostUsed(); @Override List<Module> getMostRecentlyUsed(); @Override void clear(); @Override long getTotalUsage();  }### Answer:
@Test public void getTotalUsage() { injector.instance(StatefulPreferencesUsageService.class).getTotalUsage(); verify(injector.instance(PreferencesUsageDataStore.class)).getTotalUsage(); }