What It Means to Mock: Isolating Units for Testing

Mockito is a fantastic mock library for Java. I’m fascinated by how easy it is to use, compared to other things out there in the Java. To someone who is new to unit testing, the idea of mock objects can be confusing to say the least. However, in the real world, software has dependencies. We have action classes that depend on services and services that depend on data access objects (DAOs) and the list goes on. The idea of unit testing is that we want to test our code without testing the dependencies. This test allows you to verify that the code being tested works, regardless of it's dependencies. The theory is that if the code I write works as designed and my dependencies work as designed, then they should work together as designed.

          If you want to create unit tests to test your code, having an Interface that defines the signature of your Dao also lets you create a "mock"  Dao object that you can use in your tests. 

As a template, it’s a good practice to view tests like a BDD style test.

// Given

// When

// Then

The code below would be an example of this: 

• Add the Mockito dependency to your pom.xml: 

org.mockito
mockito-all
1.8.4
test 

• Mockito in JUnit test:

  import static org.mockito.Mockito.*;
  //...
  @Test
  public void testMock() {

       // Given
      
  

  Map mapMock = mock(Map.class);

  
  

  // When
  when(mapMock.get("1")).thenReturn("1");
  when(mapMock.get("2")).thenReturn("2");
  
  Object o = new Object();
  mapMock.put("anyObject", o);

  
  

  //Then

   assertEquals("firstValue", mapMock.get("1"));

  assertEquals("secondValue", mapMock.get("2"));
  
  verify(mapMock).get("1");
  verify(mapMock).get("1");
  
  verify(mapMock).put("anyObject", o);
  }
  

That’s it – all you need to know to get started. Mock objects are a very valuable tool in testing. They provide you with the ability to test what you write without having to address dependency concerns.