在JMock中访问包私有类时出现IllegalAccessError

Question

I have written a unit test using JMock 2.6.0-RC2 that makes use of several package private classes. For some reason, this causes an IllegalAccessError :

java.lang.IllegalAccessError: tried to access class foo.PackagePrivateClass from class $Proxy6
    at $Proxy6.getInstance(Unknown Source)
    at foo.UsingClass.<init>(UsingClass.java:6)
    at foo.FailingTest.testFailure(FailingTest.java:29)

I have uploaded a minimal Maven project that demonstrates the issue to here: http://dl.dropbox.com/u/108474287/example-project.zip . The relevant code is also shown below (it's fairly concise).

Why am I seeing an error in my test? The test class is part of the same package as the tested classes, so I would not expect access control to be an issue.

Some interesting observations:

1. If I change ExampleInterface to be package private (rather than public), the problem goes away. Sadly, in my real-life project this is not a possibility.

2. The exception only occurs if I return a value from my mock object. Those who download my example project will see another test in which null is returned; this test passes.

3. If I move the all the classes into the default package, the tests pass! If all the classes remain in package foo , the tests fail.

Below are the files contained in my project. The ZIP I linked to above is a small Maven project that houses all of these.

I have also posted this question to the JMock developer list. I will update this question if I receives answers there (and vice versa).

---

FailingTest.java

package foo;

// Imports omitted

@RunWith(JMock.class)
public class FailingTest {

  private static final PackagePrivateClass EXAMPLE_INSTANCE = 
      new PackagePrivateClass();

  public Mockery context = new JUnit4Mockery();

  @Test
  public void testFailure() {
    final ExampleInterface exampleInterface = context
        .mock(ExampleInterface.class);

    context.checking(new Expectations() {
      {
        oneOf(exampleInterface).getInstance(); 
        will(returnValue(EXAMPLE_INSTANCE));
      }
    });

    new UsingClass(exampleInterface); <-- exception thrown from constructor
  }
}

ExampleInterface.java

package foo;

public interface ExampleInterface {
  PackagePrivateClass getInstance();
}

PackagePrivateClass.java

package foo;

class PackagePrivateClass {

  PackagePrivateClass() {}

  @Override
  public String toString() {
    return "Hello, World!";
  }
}

UsingClass.java

package foo;

class UsingClass {

  UsingClass(ExampleInterface exampleInterface) {
    PackagePrivateClass bar = exampleInterface.getInstance(); // <--- exception
    System.out.println(bar);                                  // originates here
  }
}

Answer 1

To provide an update for future readers....

Currently, I believe this is a bug in JMock. I've filed it on the JMock github page: https://github.com/jmock-developers/jmock-library/issues/43 . No responses yet (nor to my comment on the mailing list).

I've since switched to Mockito , which is able to handle exactly the same situation without error.