jMock in 5 minutes

JMock makes it easy to mock up objects in unit tests.

Create Mock Objects

Use annotations @Rule and @Mock to create mock objects.

import org.jmock.auto.Mock;

import org.jmock.integration.junit4.JUnitRuleMockery;

import org.junit.Rule;

import org.junit.Test;

public class GettingStartedTest {

    //The rule context field must be public

    @Rule public final JUnitRuleMockery context = new JUnitRuleMockery();

    @Mock private Runnable runnable;

   

   @Test

   public void testInvocation() {  

        ...  

   }

    

}

Alternatively, you can define the mock object as follows:

Mockery context = new JUnit4Mockery();

private Runnable runnable = context.mock(Runnable.class);

Set Expectations on Invocations

    @Test

    public void testInvocation() {    

       

    // Set invocation expectations.

    // You can use:

    //     oneOf, exactly(n).of,

    //     atLeast(n).of, atMost(n).of, between(min, max).of

    //     allowing, never

    // For details, see http://www.jmock.org/cardinality.html

    context.checking(new Expectations() {{

      //The method runnable.run() will be invoked once and once only.

      oneOf (runnable).run();

        }});

             

    runnable.run();

     }

Mock (or Set Expectations on) Return Results

import static org.junit.Assert.*;

import java.util.Map;

import org.jmock.Expectations;

import org.jmock.auto.Mock;

import org.jmock.integration.junit4.JUnitRuleMockery;

import org.junit.Rule;

import org.junit.Test;

public class MockResultTest {

@Rule public final JUnitRuleMockery context = new JUnitRuleMockery();

@Mock private Map map;

   

    @Test

    public void testMockedResults() {    

       

    context.checking(new Expectations() {{

       

      oneOf(map).get("Jason");

      will(returnValue(10));

     

      oneOf(map).get("Jay");

      will(returnValue(5));

     

      // You cannot define as follows:

      //    allowing(map).get("Jason"); ...

      //    allowing(map).get("Jay"); ...

      // The 2nd allowing does not take effect.

     

      allowing(map).remove(with(any(String.class)));

      will(returnValue(100));

        }});

             

    assertEquals(map.get("Jason"), 10);

    assertEquals(map.get("Jay"), 5);

    assertEquals(map.remove("foo"), 100);

  }

}

References

• jMock Cheat Sheet