Asserting a changed state on a mocked object

I would like to unit test a function that takes a certain object as input, processes it and when it finished, the state of that object should have been changed to a certain value.

As I want to do "real" unit testing (as I understand it), I only want to use the class that is providing the processing function, and mock all other classes used. To fulfill this requirement I need to mock the object that is being processed; but when it is only a mock, it has no real state anymore that could be changed.

Example pseudocode:

object = createMock('SomeClassName');
object.whenReceives('getState').shouldReturn(0);

Processor.process(object);
assertEquals(expected = 1, actual = object.getState());

The problem is that I need to mock the "getState" method to prepare the starting state for the test, and so afterwards I cannot use the real method anymore. Do you know how can I achieve this, or how I should change the design of the test?

PS: I am actually using PHPUnit and Mockery.

Thank you for any advice.