Automatic mock creation with JUnit & Mockito
February 19th, 2009
Mockito is really a great mocking framework. It is based on a powerful stubbing and verification mecanism. Using it is as simple as this:
import static org.mockito.Mockito.*;
List mockedList = mock(List.class);
mockedList.add("one");
mockedList.clear();
verify(mockedList).add("one");
verify(mockedList).clear();
A handy tool provided by Mockito is a custom JUnit runner that automatically creates mock for fields tagged with @Mock annotation:
@RunWith(MockitoJUnit44Runner.class)
public class ArticleManagerTest {
@Mock private ArticleCalculator calculator;
@Mock private ArticleDatabase database;
@Mock private UserProvider userProvider;
private ArticleManager manager;
In our team, we came up with an even simpler solution. All mock names should start with mock to ease test code readability. So we coded a custom Runner that doesn’t need the @Mock annotation.
@RunWith(AutoMockRunner.class)
public class ArticleManagerTest {
private ArticleCalculator mockCalculator;
private ArticleDatabase mockDatabase;
private UserProvider mockUserProvider;
private ArticleManager manager;
Here is the runner implementation:
public class AutoMockRunner extends BlockJUnit4ClassRunner {
public AutoMockRunner(Class< ?> clazz) throws InitializationError {
super(clazz);
}
@Override
protected Object createTest() throws Exception {
Object clazz = super.createTest();
for (Class< ?> c = clazz.getClass(); c != Object.class; c = clazz.getSuperclass()) {
scan(testClass, c);
}
return clazz;
}
private static void scan(Object testClass, Class< ?> clazz) {
for (Field field : clazz.getDeclaredFields()) {
if (field.getName().startsWith("mock")) {
Object mock = Mockito.mock(field.getType(), field.getName());
try {
if (field.isAccessible()) {
field.set(testClass, mock);
} else {
field.setAccessible(true);
try {
field.set(testClass, mock);
} finally {
field.setAccessible(false);
}
}
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
}
}
}
