What's the best mock framework for Java? [closed]

Question

I've had good success using Mockito.

When I tried learning about JMock and EasyMock, I found the learning curve to be a bit steep (though maybe that's just me).

I like Mockito because of its simple and clean syntax that I was able to grasp pretty quickly. The minimal syntax is designed to support the common cases very well, although the few times I needed to do something more complicated I found what I wanted was supported and easy to grasp.

Here's an (abridged) example from the Mockito homepage:

import static org.mockito.Mockito.*;

List mockedList = mock(List.class);
mockedList.clear();
verify(mockedList).clear();

It doesn't get much simpler than that.

The only major downside I can think of is that it won't mock static methods.

I am the creator of PowerMock so obviously I must recommend that! :-)

PowerMock extends both EasyMock and Mockito with the ability to mock static methods, final and even private methods. The EasyMock support is complete, but the Mockito plugin needs some more work. We are planning to add JMock support as well.

PowerMock is not intended to replace other frameworks, rather it can be used in the tricky situations when other frameworks does't allow mocking. PowerMock also contains other useful features such as suppressing static initializers and constructors.

The JMockit project site contains plenty of comparative information for current mocking toolkits.

In particular, check out the feature comparison matrix, which covers EasyMock, jMock, Mockito, Unitils Mock, PowerMock, and of course JMockit. I try to keep it accurate and up-to-date, as much as possible.

I've been having success with JMockit.

It's pretty new, and so it's a bit raw and under-documented. It uses ASM to dynamically redefine the class bytecode, so it can mock out all methods including static, private, constructors, and static initializers. For example:

import mockit.Mockit;

...
Mockit.redefineMethods(MyClassWithStaticInit.class,
                       MyReplacementClass.class);
...
class MyReplacementClass {
  public void $init() {...} // replace default constructor
  public static void $clinit{...} // replace static initializer
  public static void myStatic{...} // replace static method
  // etc...
}

It has an Expectations interface allowing record/playback scenarios as well:

import mockit.Expectations;
import org.testng.annotations.Test;

public class ExpecationsTest {
  private MyClass obj;

  @Test
  public void testFoo() {
    new Expectations(true) {
      MyClass c;
      {
        obj = c;
        invokeReturning(c.getFoo("foo", false), "bas");
      }
    };

    assert "bas".equals(obj.getFoo("foo", false));

    Expectations.assertSatisfied();
  }

  public static class MyClass {
    public String getFoo(String str, boolean bool) {
      if (bool) {
        return "foo";
      } else {
        return "bar";
      }
    }
  }
}

The downside is that it requires Java 5/6.

You could also have a look at testing using Groovy. In Groovy you can easily mock Java interfaces using the 'as' operator:

def request = [isUserInRole: { roleName -> roleName == "testRole"}] as HttpServletRequest 

Apart from this basic functionality Groovy offers a lot more on the mocking front, including the powerful MockFor and StubFor classes.

http://docs.codehaus.org/display/GROOVY/Groovy+Mocks