java.lang.IllegalStateException: missing behavior definition for the preceding method call getMessage("title")

Answer 1

You need to call EasyMock.replay(mock) before calling the method under test. After calling the method under test you can call EasyMock.verify(mock) to verify the mock is called.

Next you need to add another expect call with the "title" argument since you call it twice.

Code:

EasyMock.expect(mockMessageResourse.getMessage("title")).andReturn("title");    
EasyMock.expect(mockMessageResourse.getMessage("ClassB.title")).andReturn("someTitle");
EasyMock.replay(mockMessageResourse);
clientMessages = new ClientMessages(mockMessageResourse);

classToTest = new ClassB();

Assert.assertEquals("someTitle" , classToTest.getDisplayName());
EasyMock.verify(mockMessageResourse);