Using Mockito with JUnit 5

Igor Stojanovski -

Since version 2.16.3 Mockito has official support for Junit5. Using Mockito with JUnit now is even easier than before. Previously I kept forgetting what rule I was supposed to use for injecting the mocks, and how I set the strictness again? Plus the extra field in each test class!

Mockito with JUnit 5 example

The newly introduced extension is not part of the mockito-core package. In order to use it, you will have to add a separate dependency:

<dependency>
    <groupId>org.mockito</groupId>
    <artifactId>mockito-junit-jupiter</artifactId>
    <version>${mockito.version}</version>
    <scope>test</scope>
</dependency>

The extension will initialize all the fields annotated with @Mock. If you want to set the strictness of the stubs, use the MockitoSetting annotations. In the sample code, I set the strictness to STRTICT_STUBS although that is already the default.

@ExtendWith(MockitoExtension.class)
@MockitoSettings(strictness = Strictness.STRICT_STUBS)
class ChatEngineTest {

    @Mock
    private MessageSender messageSender;

    @Test
    public void shouldUseMessageSenderToSendMessage() {
        ChatEngine chatEngine = new ChatEngine(messageSender);
        String messageToSend = "Hello!";

        chatEngine.say(messageToSend);
        when(messageSender.send(messageToSend)).thenReturn(OK);

        assertThat(messageSender.send(messageToSend)).isEqualTo(OK);
    }

}

How does the extension work?

I previously spoke about the JUnit 5 extension model, and MockitoExtension is a great example of putting that into practice. It uses three extension points:

  • TestInstancePostProcessor: to set the test instance.
  • BeforeEachCallback: to create the Mockito session and initialize all the mocks.
  • AfterEachCallback: to remove the previously created session.

Nice and easy.