lesson11.md

Lesson 11: Spring Unit Testing with Mockito

Overview

Ideally, when writing unit tests, we should only focus on the class under test and mock the dependencies. We will now write a test for the same class using Mockito.

Demonstrated Concepts

mockito-core dependency

To test using the Mockito framework, we need the mockito-core dependency, which can be added to pom.xml as follows:

<dependency>
  <groupId>org.mockito</groupId>
  <artifactId>mockito-core</artifactId>
  <scope>test</scope>
</dependency>

Note that this dependency is automatically available if springboot-starter-test is included in the pom.xml file.

Mocking an interface

Mockito can be used when we want to test the interface with different kinds of data. We will mock the interface using the @Mock annotation as follows:

@Mock
private Filter mockFilter;

This mockFilter can be injected in the bean using the @InjectMocks annotation.

@InjectMocks
private RecommenderImplementation recommenderImpl;

We need the @ExtendWith annotation with MockitoExtension.class to enable the use of the annotations mentioned above.

The test for a case when no recommendation is returned is given below:

@Test
void testRecommendMovies_noRecommendationsFound() {
    when(mockFilter.getRecommendations("Finding Dory")).thenReturn(new String[] {});
    assertArrayEquals(new String[] {}, recommenderImpl.recommendMovies("Findng Dory"));
}

Here, we are intercepting the call to getRecommendations and returning a hard coded result without calling the interface method.

Using Mockito, the tests take less time as there is no need to load the application context. Whenever possible, try to avoid using Spring in unit testing as it makes the turnaround time longer.

Spring also provides annotations for testing a particular layer like @WebMvcTest and @DataJpaTest that load only a part of the context and mock the rest of the dependencies.