[Spring Boot] Introduce to Mockito

We have the implemetion: 

@SpringBootApplication
public class MockitoDemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(MockitoDemoApplication.class, args);
    }

}

public class SomeBusinessImpl {
    private DataService dataService;

    public SomeBusinessImpl(DataService dataService ){
        super();
        this.dataService = dataService;
    }

    public int findTheGreatestFromAllData() {
        int[] data = dataService.retieveAllData();
        int greatest = Integer.MIN_VALUE;
        for (int value : data) {

            if (value > greatest) {
                greatest = value;
            }
        }
        return greatest;
    }
}


public interface DataService {
    int[] retieveAllData();
}

And we want to test agaisnst it:

import org.junit.Test;

import static org.junit.Assert.assertEquals;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;

public class SomeBusinessMockTests {

    @Test
    public void testFindTheGreatestFromAllData() {
        DataService mockService = mock(DataService.class);
        when( mockService.retieveAllData()).thenReturn(new int[] {24, 6, 15});

        SomeBusinessImpl businessImpl = new SomeBusinessImpl(mockService);
        int result = businessImpl.findTheGreatestFromAllData();
        assertEquals(24, result);
    }
}