Unit Testing with JUnit & Mockito – Code Examples

unit testing

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.

cardIsNotCreatedIfMandatoryUserDetailsNotProvided
cardIsNotCreatedIfCardFailedToPersistInDatabase
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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