A JUnit rule to easily override Dagger 2 objects
More info about testing using Dagger 2 and Mockito are available in this Medium post.
Overriding an object managed by Dagger 2 is not easy, you need to define a TestModule and, if you want to inject your test object, a TestComponent.
Using a DaggerMockRule it's possible to override easily the objects defined in a Dagger module:
public class MainServiceTest {
@Rule public DaggerMockRule<MyComponent> rule = new DaggerMockRule<>(MyComponent.class, new MyModule())
.set(new DaggerMockRule.ComponentSetter<MyComponent>() {
@Override public void setComponent(MyComponent component) {
mainService = component.mainService();
}
});
@Mock RestService restService;
@Mock MyPrinter myPrinter;
MainService mainService;
@Test
public void testDoSomething() {
when(restService.getSomething()).thenReturn("abc");
mainService.doSomething();
verify(myPrinter).print("ABC");
}
}When DaggerMockRule rule is instantiated, it looks for all @Mock annotated fields in your test class
and it replaces them with Mockito mocks if there is a provider method in your module for that class.
Then it uses all the test fields to override the objects defined in the Dagger configuration.
In this example
MyModule
contains two methods to provide RestService and MyPrinter objects. Behind the scenes, the
DaggerMockRule rule dynamically creates a new module that overrides MyModule, it returns the mocks
for restService and myPrinter defined in the test instead of the real objects, like this:
public class TestModule extends MyModule {
@Override public MyPrinter provideMyPrinter() {
return Mockito.mock(MyPrinter.class);
}
@Override public RestService provideRestService() {
return Mockito.mock(RestService.class);
}
}DaggerMock can't override Dagger objects that are defined using Inject annotation, since version 0.6
you get a runtime error if the test contains a field of a class that is not defined in a module.
A DaggerMockRule can also be used in an Espresso test:
public class MainActivityTest {
@Rule public DaggerMockRule<MyComponent> daggerRule = new DaggerMockRule<>(MyComponent.class, new MyModule())
.set(new DaggerMockRule.ComponentSetter<MyComponent>() {
@Override public void setComponent(MyComponent component) {
App app = (App) InstrumentationRegistry.getInstrumentation().getTargetContext().getApplicationContext();
app.setComponent(component);
}
});
@Rule public ActivityTestRule<MainActivity> activityRule = new ActivityTestRule<>(MainActivity.class, false, false);
@Mock RestService restService;
@Mock MyPrinter myPrinter;
@Test
public void testCreateActivity() {
when(restService.getSomething()).thenReturn("abc");
activityRule.launchActivity(null);
verify(myPrinter).print("ABC");
}
}In a similar way a DaggerMockRule can be used in a Robolectric test:
@RunWith(RobolectricGradleTestRunner.class)
@Config(constants = BuildConfig.class, sdk = 21)
public class MainActivityTest {
@Rule public final DaggerMockRule<MyComponent> rule = new DaggerMockRule<>(MyComponent.class, new MyModule())
.set(new DaggerMockRule.ComponentSetter<MyComponent>() {
@Override public void setComponent(MyComponent component) {
((App) RuntimeEnvironment.application).setComponent(component);
}
});
@Mock RestService restService;
@Mock MyPrinter myPrinter;
@Test
public void testCreateActivity() {
when(restService.getSomething()).thenReturn("abc");
Robolectric.setupActivity(MainActivity.class);
verify(myPrinter).print("ABC");
}
}In the first example we have used a ComponentSetter subclass to retrieve an object from the component:
@Rule public DaggerMockRule<MyComponent> rule = new DaggerMockRule<>(MyComponent.class, new MyModule())
.set(new DaggerMockRule.ComponentSetter<MyComponent>() {
@Override public void setComponent(MyComponent component) {
mainService = component.mainService();
}
});
MainService mainService;Since DaggerMock 0.6 this code can be written in an easier way using InjectFromComponent annotation:
public class MainServiceTest {
@Rule public final DaggerMockRule<MyComponent> rule = new DaggerMockRule<>(MyComponent.class, new MyModule());
@Mock RestService restService;
@Mock MyPrinter myPrinter;
@InjectFromComponent MainService mainService;
@Test
public void testDoSomething() {
when(restService.getSomething()).thenReturn("abc");
mainService.doSomething();
verify(myPrinter).print("ABC");
}
}Many objects managed by Dagger are only injected in other objects and are not exposed in a component. For example if the MainService object is injected in MainActivity we can use the following annotation:
@InjectFromComponent(MainActivity.class) MainService mainService;A MainActivity object is created using reflection, the inject method is invoked on this object and then the mainService field is extracted and used to populate the test field.
It's easy to create a DaggerMockRule subclass to avoid copy and paste and simplify the test code:
public class MyRule extends DaggerMockRule<MyComponent> {
public MyRule() {
super(MyComponent.class, new MyModule());
set(new DaggerMockRule.ComponentSetter<MyComponent>() {
@Override public void setComponent(MyComponent component) {
App app = (App) InstrumentationRegistry.getInstrumentation().getTargetContext().getApplicationContext();
app.setComponent(component);
}
});
}
}The final test uses the rule subclass:
public class MainActivityTest {
@Rule public MyRule daggerRule = new MyRule();
@Rule public ActivityTestRule<MainActivity> activityRule = new ActivityTestRule<>(MainActivity.class, false, false);
@Mock RestService restService;
@Mock MyPrinter myPrinter;
@Test
public void testCreateActivity() {
when(restService.getSomething()).thenReturn("abc");
activityRule.launchActivity(null);
verify(myPrinter).print("ABC");
}
}Since version 0.6 Dagger subcomponents are supported by DaggerMock with a limitation: subcomponent module must be passed as parameter in subcomponent creation method. For example if the subcomponent is defined as follows:
@Subcomponent(modules = MainActivityModule.class)
public interface MainActivityComponent {
void inject(MainActivity mainActivity);
}The method in the main component that creates the subcomponent must be defined using a module parameter:
@Singleton
@Component(modules = AppModule.class)
public interface AppComponent {
MainActivityComponent activityComponent(MainActivityModule module);
}Subcomponent support doesn't work on Dagger 2.0, you need to use Dagger version 2.1+. A complete example is available here.
DaggerMock is available on JitPack, add the JitPack repository in your build.gradle (in top level dir):
repositories {
jcenter()
maven { url "https://jitpack.io" }
}and the dependency in the build.gradle of the module:
dependencies {
testCompile 'com.github.fabioCollini:DaggerMock:0.6.3'
//and/or
androidTestCompile 'com.github.fabioCollini:DaggerMock:0.6.3'
}Copyright 2016 Fabio Collini
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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