How to load the properties from application.properties in Mockito test

Question

I am trying to write a unit test case to test the method, but I encounter a problem.

here is the sample code:

MyService1

@Service
public class MyService1 {

    @Autowired
    private ServiceProperties serviceProperties;

    public void getMyLanguage(){
        String language =  serviceProperties.getLocale().getLanguage();
        printSomething(language);
    }

    private void printSomething(String input){
        System.out.print("your current language is " + input);
    }
}

ServiceProperties

import org.springframework.boot.context.properties.ConfigurationProperties;

import java.util.Locale;

@ConfigurationProperties(prefix = "conversation")
public class ServiceProperties {

    private ServiceProperties(){};

    private Locale locale;

    public Locale getLocale(){

        return locale;

    }
}

application.properties

conversation.locale=en_US

Here is my test case:

import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.MockitoJUnitRunner;

import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;

@RunWith(MockitoJUnitRunner.class)
public class MyService1Test {
    @Mock
    private ServiceProperties serviceProperties;

    @InjectMocks
    private MyService1 myService1;

    @Test
    public void getMyLanguage(){
        when(serviceProperties.getLocale().getLanguage()).thenReturn("EN");
        myService1.getMyLanguage();
        verify(myService1).getMyLanguage();
    }
}

the test will trigger nullpointerexception, because the properties for locale are not loaded in test, if I don't want to start the server(use @SpringBootTest annotation) to load the context, is there any way to solve this problem, can anyone help?

Answer 1

The problem is at this line:

when(serviceProperties.getLocale().getLanguage()).thenReturn("EN");

Because serviceProperties is mocked, serviceProperties.getLocale() is equal to null . So you get NullPointerException when serviceProperties.getLocale().getLanguage() is called.

One workaround would be as follows:

@RunWith(MockitoJUnitRunner.class)
public class MyService1Test {
    @Mock
    private ServiceProperties serviceProperties;
    @InjectMocks
    private MyService1 myService1;

    @Test
    public void getMyLanguage(){
        when(serviceProperties.getLocale()).thenReturn(new Locale("EN"));
        myService1.getMyLanguage();
        verify(myService1).getMyLanguage();
    }
}

Answer 2

Field injection is not convenient for testing. You can use constructor injection

@Service
public class MyService {


    private final ServiceProperties serviceProperties;

    @Autowired
    public MyService(ServiceProperties serviceProperties) {
        this.serviceProperties = serviceProperties;
    }
    //...
}

And then you will be able to inject mocks before each test

@RunWith(MockitoJUnitRunner.class)
public class MyService1Test {
    @Mock
    private ServiceProperties serviceProperties;

    private MyService1 myService1;

    @Before
    public void createService(){
        myService1 = new MyService1(serviceProperties);
    }
}