Unit Testing with JUnit & Mockito – Code Examples

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The article presents quick code example for doing unit testing with JUnit & Mockito mocking framework. It also represents unit testing naming convention where features text is used for naming the test methods thereby representing test class as alternate documentation for the class under test.

Following is done while defining Mock member variables

  • Use @Mock annotation ahead of member variable definitions

Following are steps done in the setup method:

  • Initialize the mock using MockitoAnnotations.initMocks(this);
  • Object of class under test is initialized with the mock objects

Following steps are used in each of the unit test methods:

  • Create/Initialize required objects for working with mocks and methods under test
  • Set the mock behavior on dependent objects
  • Execute the method under test 
  • Perform assertions
  • Verify the program execution path by checking on whether a method is invoked or not

The code below represents the class under test and the unit test written to test the class. Take a look the unit test names which represents the card creation function and the scenarios in which it would pass or fail. Following are names. These are unlike the unit test names which uses the function name with state and execution result. I find it easy to understand the unit tests in this way.

  1. cardIsNotCreatedIfMandatoryUserDetailsNotProvided
  2. cardIsNotCreatedIfCardFailedToPersistInDatabase
  3. cardIsCreatedIfAllBusinessRulesAreSatisfied

 

Class Under Test

 

public CPResult createCard( Card card ) {

	CPResult cpResult = new CPResult();

	if( card != null ) {
		boolean validated = cdValidator.validate( card );
		if( validated ) {
			boolean cardCreated = cardDAO.createCard( card );
			if( !cardCreated ) {					
				cpResult.setMessage( CPResult.CARD_PERSISTENCE_FAILURE_MESSAGE );
			}
		} else {				
			cpResult.setMessage( CPResult.CARD_VALIDATION_FAILURE_MESSAGE );
		}
	} else {			
		cpResult.setMessage( CPResult.CARD_FATAL_ERROR_MESSAGE );
	}
	if( cpResult.getMessage() != null ) {
		cpResult.setStatus( CPResult.CARD_OPERATION_FAILURE );
	}
	return cpResult;		
}

 

Unit Test Class

 

public class PrepaidCardProcessorTest {

	private PrepaidCardProcessor prepaidCP;	
	@Mock private CardDetailsValidator cdValidator;
	@Mock private CardDAO cardDAO;

	@Before
	public void setUp() throws Exception {
		MockitoAnnotations.initMocks(this);
		prepaidCP = new PrepaidCardProcessor();
		prepaidCP.setCdValidator( cdValidator );
		prepaidCP.setCardDAO( cardDAO );
	}

	@After
	public void tearDown() throws Exception {
	}

	@Test
	public void cardIsNotCreatedIfMandatoryUserDetailsNotProvided() {
		// Create required objects for working with mocks and methods under test
		//
		Card card = new Card();		
		// Set the mock behavior on dependent objects
		//
		Mockito.when( cdValidator.validate( card ) ).thenReturn( false );
		// Execute the method under test 
		//
		CPResult cpresult = prepaidCP.createCard( card );
		// Perform assertions
		//
		assertTrue( cpresult.getStatus() == CPResult.CARD_OPERATION_FAILURE );
		assertTrue( cpresult.getMessage().equals( CPResult.CARD_VALIDATION_FAILURE_MESSAGE ) );
		// Verify the program execution path by checking on whether a method is invoked or not
		//
		Mockito.verify(cdValidator).validate(card);
		Mockito.verify(cardDAO, Mockito.never() ).createCard( card );
	}

	@Test
	public void cardIsNotCreatedIfCardFailedToPersistInDatabase() {
		// Create required objects for working with mocks and methods under test
		//
		Card card = new Card();		
		// Set the mock behavior on dependent objects
		//
		Mockito.when( cdValidator.validate( card ) ).thenReturn( true );
		Mockito.when( cardDAO.createCard( card ) ).thenReturn( false );
		// Execute the method under test 
		//
		CPResult cpresult = prepaidCP.createCard( card );
		// Perform assertions
		//
		assertTrue( cpresult.getStatus() == CPResult.CARD_OPERATION_FAILURE );
		assertTrue( cpresult.getMessage().equals( CPResult.CARD_PERSISTENCE_FAILURE_MESSAGE ) );
		// Verify the program execution path by checking on whether a method is invoked or not
		//
		Mockito.verify(cdValidator).validate(card);
		Mockito.verify(cardDAO ).createCard( card );
	}

	@Test
	public void cardIsCreatedIfAllBusinessRulesAreSatisfied() {
		// Create required objects for working with mocks and methods under test
		//
		Card card = new Card();		
		// Set the mock behavior on dependent objects
		//
		Mockito.when( cdValidator.validate( card ) ).thenReturn( true );
		Mockito.when( cardDAO.createCard( card ) ).thenReturn( true );
		// Execute the method under test 
		//
		CPResult cpresult = prepaidCP.createCard( card );
		// Perform assertions
		//
		assertTrue( cpresult.getStatus() == CPResult.CARD_OPERATION_SUCCESS );	
		assertNull( cpresult.getMessage() );
		// Verify the program execution path by checking on whether a method is invoked or not
		//
		Mockito.verify(cdValidator).validate(card);
		Mockito.verify(cardDAO ).createCard( card );
	}

}

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Ajitesh Kumar

Ajitesh Kumar

Ajitesh has been recently working in the area of AI and machine learning. Currently, his research area includes Safe & Quality AI. In addition, he is also passionate about various different technologies including programming languages such as Java/JEE, Javascript and technologies such as Blockchain, mobile computing, cloud-native technologies, application security, cloud computing platforms, big data etc.

He has also authored the book, Building Web Apps with Spring 5 and Angular.
Ajitesh Kumar

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