Spring Boot Integration Testing with mocked Services/Components

Question

Situation and Problem: In Spring Boot, how can I inject one or more mocked classes/beans into the application to do an integration test? There are a few answers on StackOverflow, but they are focused on the situation before Spring Boot 1.4 or are just not working for me.

The background is, that in the code bellow the implementation of Settings relies on third party servers and other external systems. The functionality of Settings is already tested in a unit test, so for a full integration test I want to mock out the dependency to these servers or system and just provide dummy values.

MockBean will ignore all existing bean definitions and provide a dummy object, but this object doesn't provide a method behavior in other classes that inject this class. Using the @Before way to set the behavior before a test doesn't influence the injected object or isn't injected in other application services like AuthenticationService.

My question: How can I inject my beans into the application context? My test:

package ch.swaechter.testapp;

import ch.swaechter.testapp.utils.settings.Settings;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mockito;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.mock.mockito.MockBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Primary;
import org.springframework.test.context.junit4.SpringRunner;

@TestConfiguration
@RunWith(SpringRunner.class)
@SpringBootTest(classes = {MyApplication.class})
public class MyApplicationTests {

    @MockBean
    private Settings settings;

    @Before
    public void before() {
        Mockito.when(settings.getApplicationSecret()).thenReturn("Application Secret");
    }

    @Test
    public void contextLoads() {
        String applicationsecret = settings.getApplicationSecret();
        System.out.println("Application secret: " + applicationsecret);
    }
}

And bellow a service that should use the mocked class, but doesn't receive this mocked class:

package ch.swaechter.testapp;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class AuthenticationServiceImpl implements AuthenticationService {

    private final Settings settings;

    @Autowired
    public AuthenticationServiceImpl(Settings settings) {
        this.settings = settings;
    }

    @Override
    public boolean loginUser(String token) {
        // Use the application secret to check the token signature
        // But here settings.getApplicationSecret() will return null (Instead of Application Secret as specified in the mock)!
        return false;
    }
}

Answer 1

Looks like you are using Settings object before you specify its mocked behavior. You have to run

Mockito.when(settings.getApplicationSecret()).thenReturn("Application Secret");

during configuration setup. For preventing that you can create special configuration class for test only.

@RunWith(SpringRunner.class)
@SpringBootTest(classes = {MyApplication.class, MyApplicationTest.TestConfig.class})
public class MyApplicationTest {

    private static final String SECRET = "Application Secret";

    @TestConfiguration
    public static class TestConfig {
        @Bean
        @Primary
        public Settings settingsBean(){
            Settings settings = Mockito.mock(Settings.class);
            Mockito.when(settings.getApplicationSecret()).thenReturn(SECRET);
            Mockito.doReturn(SECRET).when(settings).getApplicationSecret();
            return settings;
        }

    }

.....

}  

Also I would recommend you to use next notation for mocking:

Mockito.doReturn(SECRET).when(settings).getApplicationSecret();

It will not run settings::getApplicationSecret