如何在 JUnit 测试中使用 Mockito？

Question

The class to test is a self-made LinkedList. In one specific method, I just want to use Mockito to avoid adding extra element to the list , that could affect other test methods. But I don't believe I use it in a right way. Any suggestions?

public class AppTest {

private LinkedList<Integer> link;
@Before
public void setUp() {
    //just want to populate the list with 4 elements for all tests
    link=mock(com.sed.MyLinkedList.LinkedList.class);
    link.add(111);
    link.add(222);
    link.add(333);
    link.add(444);
}

@Test
public void testApp() {     
    //add extra elements here for this specific test, shouldn't be really added to list 
    link.add(2, 900);
    //here 'when().thenReturn()' is useless
    when(link.toString()).thenReturn("[111, 222, 900, 333, 444]");
    assertEquals("[111, 222, 900, 333, 444]",link.toString());      
}

@Test(expected = ArrayIndexOutOfBoundsException.class)
public void testAppException() {
    link.add(5, 900);
}

}

Answer 1

In your tests, you are only testing a mock, but not your class. For what you mentioned, just change the setup method to instantiate the real class.

@Before
public void setUp() {
    //just want to populate the list with 4 elements for all tests
    link = new com.sed.MyLinkedList.LinkedList();
    link.add(111);
    link.add(222);
    link.add(333);
    link.add(444);
}

Before each test, the setup method is called, so you'll have a fresh list with the 4 elements in it.

Mocks are used when the class that is being tested uses collaborators. The idea behind is to isolate the class, so you are sure that any error comes from the class under test and not a collaborator.