baeldung_Junit_Guide.md

Baeldung_Junit_Guide.md

• https://aggarwal-rohan17.medium.com/simplifying-junit-mockito-and-powermock-d1392059ce87

Mockito Tutorial

• https://www.baeldung.com/mockito-series

Mockito vs EasyMock vs JMockit

• https://www.baeldung.com/mockito-vs-easymock-vs-jmockit
• 1.3. Mock Concepts and Definition
  • Dummy objects are passed around but never actually used. Usually, they are just used to fill parameter lists.
  • Fake objects have working implementations, but usually, take some shortcut that makes them not suitable for production (an in-memory database is a good example).
  • Stubs provide canned answers to calls made during the test, usually not responding at all to anything outside what’s programmed in for the test. Stubs may also record
  • information about calls, such as an email gateway stub that remembers the messages it ‘sent’, or maybe only how many messages it ‘sent’.
  • Mocks are what we are talking about here: objects pre-programmed with expectations that form a specification of the calls they are expected to receive.

Getting Started with Mockito @Mock, @Spy, @Captor and @InjectMocks

• https://www.baeldung.com/mockito-annotations
• @Mock Annotation
  • The most widely used annotation in Mockito is @Mock. We can use @Mock to create and inject mocked instances without having to call Mockito.mock manually.

      when(mockedList.size()).thenReturn(100); //both can work in mock
      doReturn(100).when(spyList).size();

• @Spy Annotation
  • @Spy annotation to spy on an existing instance.

      // when(mockedList.size()).thenReturn(100);  this is not going to work in Spy object
      doReturn(100).when(spyList).size();

• @Captor
  • make use of @Captor for the same purpose, to create an ArgumentCaptor instance

@Mock
List mockedList;

@Captor 
ArgumentCaptor argCaptor;

@Test
public void whenUseCaptorAnnotation_thenTheSame() {
    mockedList.add("one");
    Mockito.verify(mockedList).add(argCaptor.capture());

    assertEquals("one", argCaptor.getValue());
}

• @InjectMocks
  • Now let’s discuss how to use the @InjectMocks annotation to inject mock fields into the tested object automatically

Mockito ArgumentMatchers

• https://www.baeldung.com/mockito-argument-matchers

  verify(flowerService).analyze(or(eq("poppy"), endsWith("y")));

Mocking Exception Throwing using Mockito

• https://www.baeldung.com/mockito-exceptions

Mockito When/Then Cookbook

• https://www.baeldung.com/mockito-behavior
• Configure simple return behavior for mock:

MyList listMock = mock(MyList.class);
when(listMock.add(anyString())).thenReturn(false);

boolean added = listMock.add(randomAlphabetic(6));
assertThat(added).isFalse();

• Configure return behavior for mock in an alternative way:

MyList listMock = mock(MyList.class);
doReturn(false).when(listMock).add(anyString());

boolean added = listMock.add(randomAlphabetic(6));
assertThat(added).isFalse();

• Configure mock to throw an exception on a method call:

MyList listMock = mock(MyList.class);
when(listMock.add(anyString())).thenThrow(IllegalStateException.class);

assertThrows(IllegalStateException.class, () -> listMock.add(randomAlphabetic(6)));

• Configure the behavior of a method with void return type — to throw an exception:

MyList listMock = mock(MyList.class);
doThrow(NullPointerException.class).when(listMock).clear();

assertThrows(NullPointerException.class, () -> listMock.clear());

• Configure the behavior of multiple calls:

MyList listMock = mock(MyList.class);
when(listMock.add(anyString()))
  .thenReturn(false)
  .thenThrow(IllegalStateException.class);

assertThrows(IllegalStateException.class, () -> {
    listMock.add(randomAlphabetic(6));
    listMock.add(randomAlphabetic(6));
});

• Configure the behavior of a spy:

MyList instance = new MyList();
MyList spy = spy(instance);

doThrow(NullPointerException.class).when(spy).size();

assertThrows(NullPointerException.class, () -> spy.size());

• Configure method to call the real, underlying method on a mock:

MyList listMock = mock(MyList.class);
when(listMock.size()).thenCallRealMethod();

assertThat(listMock).hasSize(1);

• Configure mock method call with custom Answer:

MyList listMock = mock(MyList.class);
doAnswer(invocation -> "Always the same").when(listMock).get(anyInt());

String element = listMock.get(1);
assertThat(element).isEqualTo("Always the same");

• doAnswer
  • Using doAnswer you can do some additionals actions upon method invocation. For example, trigger a callback on queryBookTitle.
  • When you are using Spy instead of Mock
    • When using when-thenReturn on Spy Mockito will call real method and then stub your answer. This can cause a problem if you don't want to call real method, like in this sample

List list = new LinkedList();
List spy = spy(list);
// Will throw java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
when(spy.get(0)).thenReturn("java");
assertEquals("java", spy.get(0));

• Using doAnswer we can stub it safely

List list = new LinkedList();
List spy = spy(list);
doAnswer(invocation -> "java").when(spy).get(0);
assertEquals("java", spy.get(0));

• Actually, if you don't want to do additional actions upon method invocation, you can just use doReturn.

     List list = new LinkedList();
List spy = spy(list);
doReturn("java").when(spy).get(0);
assertEquals("java", spy.get(0));

Mockito Verify Cookbook

• https://www.baeldung.com/mockito-verify
  • Verify simple invocation on mock:

   List<String> mockedList = mock(MyList.class);
mockedList.size();
verify(mockedList).size();

• Verify the number of interactions with mock:

List<String> mockedList = mock(MyList.class);
mockedList.size();
verify(mockedList, times(1)).size();

• Verify no interaction with the whole mock occurred:

List<String> mockedList = mock(MyList.class);
verifyNoInteractions(mockedList);

• Verify no interaction with a specific method occurred:

List<String> mockedList = mock(MyList.class);
verify(mockedList, times(0)).size();

• Verify there are no unexpected interactions — this should fail:

List<String> mockedList = mock(MyList.class);
mockedList.size();
mockedList.clear();

verify(mockedList).size();
assertThrows(NoInteractionsWanted.class, () -> verifyNoMoreInteractions(mockedList));

• Verify the order of interactions:

List<String> mockedList = mock(MyList.class);
mockedList.size();
mockedList.add("a parameter");
mockedList.clear();

InOrder inOrder = Mockito.inOrder(mockedList);
inOrder.verify(mockedList).size();
inOrder.verify(mockedList).add("a parameter");
inOrder.verify(mockedList).clear();

• Verify an interaction has not occurred:

List<String> mockedList = mock(MyList.class);
mockedList.size();

verify(mockedList, never()).clear();

• Verify an interaction has occurred at least a certain number of times:

List<String> mockedList = mock(MyList.class);
mockedList.clear();
mockedList.clear();
mockedList.clear();

verify(mockedList, atLeast(1)).clear();
verify(mockedList, atMost(10)).clear();

• Verify interaction with the exact argument:

List<String> mockedList = mock(MyList.class);
mockedList.add("test");

verify(mockedList).add("test");

• Verify interaction with flexible/any argument:

List<String> mockedList = mock(MyList.class);
mockedList.add("test");

verify(mockedList).add(anyString());

• Verify interaction using argument capture:

List<String> mockedList = mock(MyList.class);
mockedList.addAll(Lists.<String> newArrayList("someElement"));

ArgumentCaptor<List<String>> argumentCaptor = ArgumentCaptor.forClass(List.class);
verify(mockedList).addAll(argumentCaptor.capture());

List<String> capturedArgument = argumentCaptor.getValue();
assertThat(capturedArgument).contains("someElement");

Mocking Void Methods with Mockito

• Void methods can be used with Mockito’s doNothing(), doThrow(), and doAnswer() methods, making mocking and verifying intuitive:
• https://www.baeldung.com/mockito-void-methods

Mocking Static Methods With Mockito

• https://www.baeldung.com/mockito-mock-static-methods

Mockito – Using Spies

• https://www.baeldung.com/mockito-spy

Power Mock

• https://www.baeldung.com/intro-to-powermock