3. mockito Test

public class DemoServiceTest {

    @InjectMocks
    private DemoService demoService = new DemoService();

    @Spy
    private IUsedService usedService = new UsedServiceImpl();

    @Before
    public void setUp() {

        MockitoAnnotations.initMocks(this);
        Mockito.when(usedService.echo("hello")).thenReturn("world");

    }

    @Test
    public void testEcho() {

        String result = demoService.echo2("hello");
        Assert.assertEquals("world", result);

        result = demoService.echo2("hello world");
        Assert.assertEquals("hello world", result);
    }
}