Injector (Dagger 1)

InjectedInstrumentationTest.java

public class InjectedInstrumentationTestRule implements MethodRule {

    private final Object testModule;

    public InjectedInstrumentationTestRule(Object testModule) {
        this.testModule = testModule;
    }

    @Override
    public Statement apply(final Statement statement, FrameworkMethod frameworkMethod, final Object testClassInstance) {
        return new Statement() {
            @Override
            public void evaluate() throws Throwable {
                setUpInjection(testClassInstance);
                statement.evaluate();
                tearDownInjection();
            }
        };
    }


    private void setUpInjection(Object testClass) {
        Application application = getApplication();

        List<Object> testModules = new LinkedList<>();
        testModules.addAll(Injector.getModules(application));
        testModules.add(testModule);

        ObjectGraph testObjectGraph = ObjectGraph.create(testModules.toArray());
        Injector.replaceGraph(testObjectGraph);
        testObjectGraph.inject(testClass);
    }

    private void tearDownInjection() throws Exception {
        Injector.resetFakeGraph();
    }

    private Application getApplication() {
        Instrumentation instrumentation = InstrumentationRegistry.getInstrumentation();
        return (Application) instrumentation.getTargetContext().getApplicationContext();
    }

}

Injector.java

public class Injector {

    private static ObjectGraph objectGraph;
    private static ObjectGraph fakeObjectGraph;

    public static void inject(Object target) {
        getCurrentGraph().inject(target);
    }

    public static void inject(Context target) {
        getCurrentGraph().inject(target);
    }

    public static void init(Application application) {
        objectGraph = ObjectGraph.create(getModules(application).toArray());
        objectGraph.injectStatics();
    }

    @VisibleForTesting
    public static void replaceGraph(ObjectGraph newObjectGraph) {
        fakeObjectGraph = newObjectGraph;
    }

    @VisibleForTesting
    public static void resetFakeGraph() {
        fakeObjectGraph = null;
    }

    @VisibleForTesting
    public static List<Object> getModules(Application application) {
        List<Object> modules = new LinkedList<>();
        modules.addAll(MainModulesFactory.get(application));
        modules.addAll(BuildTypeModulesFactory.get());
        return modules;
    }

    private static ObjectGraph getCurrentGraph() {
        return fakeObjectGraph == null
                ? objectGraph
                : fakeObjectGraph;
    }

}