jMock

This is a really cool open source java testing packages which works very well with JUnit. For a simple example we are going to test a publish/subscribe message system. A Publisher sends objects to zero or more Subscribers. We want to test the Publisher

import org.jmock.*;

class PublisherTest extends MockObjectTestCase {

public void testOneSubscriberReceivesAMessage() {

// set up

Publisher publisher = new Publisher();

Mock mockSubscriber = mock(Subscriber.class);

publisher.add((Subscriber) mockSubscriber.proxy());

// expectations Next we define expectations on the mock Subscriber that specify the methods that we expect to be called upon it during the test run.

final String message = "message";

mockSubscriber.expects(once()).method("receive").with( eq(message) );

publisher.publish(message);

}

}

We expect the receive method to be called with a single argument, the message that will be sent. The eq method is defined in the MockObjectTestCase class and specifies a "constraint¹" on the value of the argument passed to the subscriber: we expect the argument to be the equal to the message, but not necessarily the same object. (jMock provides several constraint types¹ that can be used to precisely specify expected argument values). We don't need to specify what will be returned from the receive method because it has a void return type.

http://www.jmock.org/

Tony