iOS OCMock partial vs class mock

Question

I am learning OCMock for iOS testing. What's the difference between "class mock" and "partial mock", and when should you use one vs the other?

http://ocmock.org/features/

Disequilibrium

Answer 1

Class mocks create objects that are pure mocks of a class instance.

Partial mocks take an instance of a class an allow you to stub any of its methods.

Suppose I have these classes:

@interface Foo : NSObject
- (void)doX;
@end
@implementation
- (void)doX
{
    NSLog(@"X");
}
@end

@interface Bar : NSObject
- (void)doA:(Foo *)foo;
- (void)doB;
@end
@implementation Bar
- (void)doA:(Foo *)foo
{
    NSLog(@"A");
    [foo doX];
    [self doB];
}
- (void)doB
{
    NSLog(@"B");
}
@end

I'm interested in testing Bar's doA: method. I expect it to call doX on a Foo object, then to call its own doB method. I would implement this using a class mock of a Foo and a partial mock of a Bar.

- (void)test_doA_shouldCall_doX_and_doB
{
    id objectUnderTest = [OCMockObject partialMockForObject:[Bar new]];
    id fooMock = [OCMockObject mockForClass:Foo.class];
    [[fooMock expect] doX];
    [[objectUnderTest expect] doB];
    // Make the call
    [objectUnderTest doA:fooMock];
    [objectUnderTest verify];
    [fooMock verify];
}

You see here that my partial mock allowed me to call the real method I wanted to test while mocking an internal call to another of its instance methods. Because I didn't need any of the real functionality of Foo, however, I used a class mock.

Killigrew

Thanks for the really helpful answer. I have two followup questions: 1) Is it true that pure mocks do not allow you to call any real methods? 2) Why couldn't you create a partial mock of Foo and then do an expect on the doX method? – Disequilibrium

1. A pure mock isn't backed by a real object, but technically you can set up any mock to call any method by using andCall or andDo -- a partial mock allows you to do andForwardToRealObject. 2. You could create a partial mock of Foo -- sometimes the creation of an object either has side effects or involves work irrelevant to your test. Additionally, a pure mock that is not a nice mock will complain when an unexpected method is called whereas a partial mock will not. – Killigrew