Yet another post about testing.
Recently I’ve been working mainly on Android projects using Java so I decided I needed to learn how to write tests in Java. For a mocking framework, Mockito seemed to be popular. I’m most familiar with NSubstitute so the syntax of Mockito seemed pretty strange at first, so before I forget it all I’ve made myself a cheat sheet.
Dependency
To start using Mockito, you need to add it in as a test dependency to your gradle script.
dependencies {
testCompile "org.mockito:mockito-core:2.8.47"
}
Further details on Mockito can be found here.
RunWith
To help keep your tests clean, use the Mockito test runner annotation with your test class;
@RunWith(MockitoJUnitRunner.class)
public class MockitoExampleTest {
}
Further details on the test runner can be found here.
Test
Creating a test is pretty straight forward; you just need to add the Test annotation to method within the test class.
@Test
public void MyTest(){
}
mock
To create a mock, there is the static mock method.
IExampleInterface exampleInterface = mock(IExampleInterface.class);
when
If you need to setup the mock to return values there is the static when method. You first specify which method you are setting up then use thenReturn to set which value you want to return.
int expectedInt = 1;
when(exampleInterface.GetNumber()).thenReturn(expectedInt);
When the method being setup has parameters, you can use exact values as the expected parameter.
String expectedString = "a string";
int inputNumber = 2;
when(exampleInterface.getString(inputNumber)).thenReturn(expectedString);
If you don’t need to be exact with the expected parameter, you can use the Mockito matchers. For example;
String expectedString = "a string";
when(exampleInterface.getString(anyInt())).thenReturn(expectedString);
Assert
Mockito plays nicely with JUnit assertions, so you can just use the standard JUnit assertions. For example;
ExampleClass exampleClass = new ExampleClass(exampleInterface);
String result = exampleClass.getResult(inputNumber);
Assert.assertEquals(expectedString, result);
verify
Verify is used to assert against the methods on a mock. You can check if a certain method was called, how many times, and with what parameters.
verify(exampleInterface, times(1)).getString(anyInt());
Captor
Captors can be use to capture the values that are passed as arguments to your mocks for further assertions. I have found them to be pretty useful for testing callbacks as you can capture the callback value, then call it in your test.
For example, you can use the Captor annotation and create a field in your test class for the captor.
@Captor
ArgumentCaptor<IHandleCallbacks> argCaptor;
Then using verify and .capture(), you can get the argument that has been passed to a mock.
verify(callbackClass, times(1)).doSomething(stringCaptor.capture(), argCaptor.capture());
Using getValue(), you can then get the value from the captor to either verify directly or in the case of a callback, call the method and assert againt what you expect to happen once the callback is called.
IHandleCallbacks callback = argCaptor.getValue();
callback.handle(1);
Example
I’ve made a small example repository on GitHub for reference.
