These are some of the useful methods and classes provided by Mockito
1. Mockito.mock()
Creates a mock of any class. By default, it will return default value for methods and fields when not mocked.
For Example:
Primitive data types such as byte
, short
, int
, long
, float
, double
, boolean
and char will return default value i.e 0
or false
Non-primitive data types such as String
, Arrays
and Classes
return null
when they are not mocked.
// with annotation
@Mock
private ClassName mock;
// Or with static method
final ClassName mock = Mockito.mock(ClassName.class);
// mock methods that returns something
Mockito.when(mock.sampleMethod()).thenReturn(sampleVal);
// mock method to throw Exception
Mockito.when(mock.sampleMethod()).thenThrow(SampleException.class);
// Mock void methods
Mockito.doNothing().when(mock).method();
// you can get invocation parameters with .thenAnswer()
Mockito.when(mock.sampleMethod(Mockito.any(OtherClass.class))).thenAnswer((Answer<ThirdClass>) invocation -> {
final OtherClass parameter1 = invocation.getArgument(0);
return thirdClassObject;
});
// Verify interactions
Mockito.verify(mock, Mockito.times(1)).sampleMethod();
// Verify, method should not be invoked even once
Mockito.verify(mock, Mockito.never()).sampleMethod2();
// Verify, no methods should be called on given mock
Mockito.verifyNoMoreInteractions(otherMockedClass);
2. Mockito.spy()
It is similar to mock()
but instead of return default value it will call the actual implementation when not mocked.
// with annotation
@Spy
private ClassName spy;
// Or with static method
final ClassName spy = Mockito.spy(ClassName.class);
// mock methods that returns something
Mockito.doReturn(value).when(spy).method();
// mock method to throw exception
Mockito.doThrow(new ExceptionClass()).when(spy).metohd();
// mock void methods
Mockito.doNothing().when(spy).method();
3. Mockito.mockStatic()
Now with Mockito 3, you can mock Classes with static methods.
try (MockedStatic<Foo> dummyStatic = Mockito.mockStatic(ClassName.class)) {
dummyStatic.when(() -> ClassName.method("param1"))
.thenReturn("someValue");
// when
System.out.println(ClassName.method("param1"));
//then
dummyStatic.verify(
() -> ClassName.method("param1"),
times(1),
);
}
4. ArgumentMatcher
Basic Rule to match any statement with Mockito is to correctly match its parameters. If any of the parameter did not match then instruction will not be mocked.
// example statement
final int addition = calculator.getAddition(2, 3);
// you have to match exact parameters, in this case (2,3)
Mockito.when(mckCalculator.getAddition(2, 3)).thenReturn(5);
// If you mock for (3,4), you mocked result will not be returned
Mockito.when(mckCalculator.getAddition(3, 4)).thenReturn(5);
// For cases, where you do not know exact parameter then you can use Mockito.anyInt()
Mockito.when(mckCalculator.getAddition(Mockito.anyInt(), Mockito.anyInt())).thenReturn(5);
Similarly we have Mockito.any()
, Mockito.anyLong()
, Mockito.anyString()
, Mockito.anyBoolean()
, Mockito.anyByte()
, Mockito.anyChar()
, Mockito.anyFloat()
, Mockito.anyDouble()
, Mockito.anyShort()
, Mockito.anyList()
, Mockito.anySet()
and Mockito.anyMap()
5. ArgumentCaptor
You can also get value of parameters of mocked methods, you can then Assert for their value.
Below is the same example of calculator class.
// example statement
final int addition = calculator.getAddition(2, 3);
// Create captor
ArgumentCaptor<Integer> argumentCaptor = ArgumentCaptor.forClass(Integer.class);
Mockito.when(mckCalculator.getAddition(argumentCaptor.capture(), argumentCaptor.capture())).thenReturn(5);
final int firstNum = argumentCaptor.getValue();
Assert.assertEquals(2, firstNum);
// You can get second num by calling getAllValues()
final int secondNum = argumentCaptor.getAllValues()[1];
Assert.assertEquals(3, secondNum);