jmock, return new object upon each call

Question

I am setting up a mock object which is supposed to return a new business object each time I call a method f() on it. If I simply say returnValue(new BusinessObj()), it will return the same reference upon each call. If I do not know how many calls there will be to f(), i.e. I cannot use onConsecutiveCalls, how can I solve this issue?

Answer 1

You need to declare a CustomAction instance in place of the standard returnValue clause:

allowing(mockedObject).f();
will(new CustomAction("Returns new BusinessObj instance") {
  @Override
  public Object invoke(Invocation invocation) throws Throwable {
    return new BusinessObj();
  }
});

Below is a self-contained unit test that demonstrates this:

import org.jmock.Expectations;
import org.jmock.Mockery;
import org.jmock.api.Invocation;
import org.jmock.integration.junit4.JMock;
import org.jmock.integration.junit4.JUnit4Mockery;
import org.jmock.lib.action.CustomAction;
import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;

@RunWith(JMock.class)
public class TestClass {

  Mockery context = new JUnit4Mockery();

  @Test
  public void testMethod() {
    final Foo foo = context.mock(Foo.class);

    context.checking(new Expectations() {
      {
        allowing(foo).f();
        will(new CustomAction("Returns new BusinessObj instance") {
          @Override
          public Object invoke(Invocation invocation) throws Throwable {
            return new BusinessObj();
          }
        });
      }
    });

    BusinessObj obj1 = foo.f();
    BusinessObj obj2 = foo.f();

    Assert.assertNotNull(obj1);
    Assert.assertNotNull(obj2);
    Assert.assertNotSame(obj1, obj2);
  }

  private interface Foo {
    BusinessObj f();
  }

  private static class BusinessObj {
  }
}