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May 23, 2022

Difference between doReturn and thenReturn in Mockito

Two ways to mock the result of a method:

1. Use doReturn followed by when
2. Use when followed by thenReturn

Use doReturn followed by when

Notice that getByName method is called after the when method.

@Test
public void test() {
    Cat cat = new Cat();
    cat.setName('Tom');
    CatServiceImpl catService = new CatServiceImpl();

    // `doReturn` followed by `when`
    // Note that `getByName` is called after`when`
    doReturn(cat).when(catService).getByName(any());

    Cat result = catService.getByName('Tom');
    assertEquals('Tom', result.getName());
}

Use when followed by thenReturn

Notice that getByName method is called within the when method.

@Test
public void test() {
    Mouse mouse = new Mouse();
    mouse.setName('Jerry');
    MouseServiceImpl mouseService = new MouseServiceImpl();

    // `when` followed by `thenReturn`
    // Note that `getByName` is called within `when`
    when(mouseService.getByName(any()).thenReturn(mouse);

    Mouse result = mouseService.getByName('Jerry');
    assertEquals('Jerry', result.getName());
}