### Question:
StatefulPreferencesUsageService implements UsageService { @Override public void incrementUsageFor(String moduleId) { dataStore.incrementUsageFor(moduleId); } @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 increment() { injector.instance(StatefulPreferencesUsageService.class).incrementUsageFor("Chuck"); verify(injector.instance(PreferencesUsageDataStore.class)).incrementUsageFor("Chuck"); }