This document provides an overview of how to use Mockito to create mock objects and define their behavior in tests. It explains how to create mocks with mock(ClassToMock.class), define return values and exceptions with when(method()).thenReturn()/thenThrow(), and verify mock interactions with verify(mock).method(). It also covers using @Mock annotation and initMocks() to initialize mocks, and matchers like eq() to verify argument matching. The document concludes with some Eclipse IDE tips to help with Mockito development.

1. Using Mockito

2. This work by
Fredrik Wendt
is licensed under a
Creative Commons
Attribution-NonCommercial-ShareAlike
3.0 Unported License
http://creativecommons.org/licenses/by-nc-sa/3.0/

3. Outline
• mock(ClassToMock.class)
• when(methodCall)
● thenReturn(value)
● thenThrow(Throwable)
• verify(mock).method(args)
• @Mock
• initMocks(this)
• assertThat(obj, matcher)
• Eclipse IDE tips

4. Why Mockito - and when?
Use Mockito to get
”smart” fake implementations
of classes or interfaces
out of your reach.

5. Classical 3A Test
@Test
public void test() throws Exception {
// Arrange
// Act
// Assert
}

6. Classical 3A Test
@Test
public void test() throws Exception {
// Arrange
UnitToTest testee = new UnitToTest();
Helper helper = new Helper();
// Act
testee.doSomething(helper);
// Assert
assertTrue(helper.somethingHappened());
}

7. Mockito ”Template” Usage
@Test
public void test() throws Exception {
// Arrange, prepare behaviour
Helper aMock = mock(Helper.class);
when(aMock.isCalled()).thenReturn(true);
// Act
testee.doSomething(aMock);
// Assert - verify interactions
verify(aMock).isCalled();
}

8. when(...).then*(...)
when(methodIsCalled).thenReturn(aValue);
when(methodIsCalled).thenThrow(anException);

9. Real Code
Properties properties = mock(Properties.class);
when(properties.get(”shoeSize”)).thenReturn(”42”);
String result = properties.get(”shoeSize”);
assertEquals(”42”, result);

10. Real Code
Properties properties = mock(Properties.class);
when(properties.get(”shoeSize”)).thenReturn(”42”);
String result = properties.get(”shoeSize”);
assertEquals(”42”, result);
// optional
verify(properties).get(”shoeSize”);

11. when(...)
when(methodIsCalled)
aMockObject.method(arguments...)
properties.get(”42”)
properties.get(anyString())
properties.get(eq(”42”))

12. thenReturn(value)
Properties properties = mock(Properties.class);
when(properties.get(”shoeSize”))
.thenReturn(”42”));
String value = properties.get(”shoeSize”);
assertEquals(”42”, value);

13. thenThrow(Exception)
Properties properties = mock(Properties.class);
when(properties.get(”shoooSize”))
.thenThrow(new IllegalArgumentException(...));
try {
properties.get(”shoooSize”);
fail(”shoooSize is misspelled”);
} catch (IllegalArgumentException e) {
// good! :)
}

14. thenReturn(...)
Properties properties = mock(Properties.class);
when(properties.get(”shoeSize”))
.thenReturn(”42”, ”43”, ”44”));
assertEquals(”42”, properties.get(”shoeSize”));
assertEquals(”43”, properties.get(”shoeSize”));
assertEquals(”44”, properties.get(”shoeSize”));
assertEquals(”44”, properties.get(”shoeSize”));
assertEquals(”44”, properties.get(”shoeSize”));
assertEquals(”44”, properties.get(”shoeSize”));

15. Creating Mock Objects
ClassToMock mockObject = mock(ClassToMock.class);
egentligen: Mockito.mock(ClassToMock.class);

16. Creating Mock Objects
ClassToMock mockObject = mock(ClassToMock.class);
@Mock
ClassToMock mockObject;
@Before
public void setup() {
MockitoAnnotations.initMocks(this);
}

17. Verifying Invocation On Mocks
// simple ”equals”
verify(properties).get(”property”);
// matchers
verify(properties).get(eq(”property”));

18. The IDE Can Help 1
• Window » Preferences » Java »
Editor » Content Assistant » Favorites
● org.junit.Assert.* assertTrue()
● org.mockito.Mockito.* mock()
● org.mockito.MockitoAnnotations @Mock
● org.mockito.BDDMockito.* given().then*()

19. The IDE Can Help 2
• Window » Preferences » Java » Editor » Templates
${staticImport:importStatic(
'org.mockito.MockitoAnnotations.
initMocks')}
@${beforeAnnotation:
newType(org.junit.Before)}
public void ${setUp}() {
initMocks(this);
${cursor}
}

20. The IDE Can Help 3
• Window » Preferences » Java » Editor » Templates
tdd
@Test
public void ${test} throws Exception {
// Arrange
// Act
// Assert
}

21. public class EmptyMatcher extends
TypeSafeMatcher<Collection <?>> {
@Override
public boolean matchesSafely(Collection<?> c) {
return c.isEmpty();
}
public void describeTo(Description desc) {
desc.appendText("empty");
}
@Factory
public static <T>
Matcher<? super Collection<?>> isEmpty() {
return new EmptyMatcher();
}
}