Java – EasyMock: Void Methods


I have a method that returns void in a class that is a dependency of the class I want to test.

This class is huge and I'm only using this single method from it.
I need to replace the implementation of this method for the test as I want it to do something different and I need to be able to access the parameters this method receives.

I cannot find a way of doing this in EasyMock. I think I know how to do it with Mockito by using doAnswer but I don't want to add another library unless absolutely necessary.

Best Solution

If I understand what you want to do correctly, you should be able to use andAnswer():

mockObject.someMethod(eq(param1), eq(param2));
expectLastCall().andAnswer(new IAnswer() {
    public Object answer() {
        //supply your mock implementation here...
        SomeClass arg1 = (SomeClass) getCurrentArguments()[0];
        AnotherClass arg2 = (AnotherClass) getCurrentArguments()[1];
        //return the value to be returned by the method (null for void)
        return null;

The EasyMock User Guide explains:

Creating Return Values or Exceptions

Sometimes we would like our mock object to return a value or throw an exception that is created at the time of the actual call. Since EasyMock 2.2, the object returned by expectLastCall() and expect(T value) provides the method andAnswer(IAnswer answer) which allows [you] to specify an implementation of the interface IAnswer that is used to create the return value or exception.

Inside an IAnswer callback, the arguments passed to the mock call are available via EasyMock.getCurrentArguments(). If you use these, refactorings like reordering parameters may break your tests. You have been warned.