KVC via keyPath is not working with OCMock

[michaelochs]

I have a object Controller that has a property that returns a mock object. I then ask Controller for valueForKeyPath: where the path is a path to the mock object's property. I can see in the debugger that valueForKeyPath: is correctly executed on the Controller and that it calls valueForKey: on the Controller object which returns the mocked object. However, the mocked object never gets a call to valueForKeyPath: or valueForKey:.

This is my mock creation:

self.reservationMock = [OCMockObject niceMockForClass:[Reservation class]];
self.sut = [[Controller alloc] initWithReservation:self.reservationMock];

The mock is stored in reservation. I evaluate a predicate with reservation.reservationMode on the sut.

I get the following calls:

• valueForKeyPath:@"reservation.reservationMode"
• valueForKey:@"reservation"

And that's it. If I do not mock the object, the evaluation continues with the following calls on the Reservation object.

• valueForKeyPath:@"reservationMode"
• valueForKey:@"reservationMode"

[erikdoe]

This does look suspicious. I'm not sure I completely understand. Could you provide a failing test?

[michaelochs]

Please see the referenced commit! Internally NSPredicate uses valueForKeyPath: to fetch the desired properties, but this does not work.

[erikdoe]

So, I keep coming back to this issue but I can't seem to find a good answer. My thoughts so far:

• For this to work in a nice way the mock would have to provide implementations of valueForKey: and valueForKeyPath:.
• It doesn't seem like a good idea to put these methods into OCClassMockObject because this would make it impossible to mock these methods.
• A solution would be to create a new subclass, maybe OCClassMockObjectWithKVSupport, but that makes the API unwieldy, and it doesn't solve the questions for partial mocks. Remember, they are a subclass of normal class mocks.
• We could have a addKeyValueCodingImplementation method that creates a dynamic subclass of the mock and adds the methods at runtime. This would address the previous two concerns. However, if we do this, what is the correct implementation of valueForKeyPath: and, especially, valueForKey:?
• We could steal the implementation of those methods from NSObject. In fact, I've tried this (see below) and it works for valueForKeyPath: but unfortunately the implementation of valueForKey: on NSObject does depend on other private methods, e.g. +_createValueGetterWithContainerClassID:key:. Adding those methods feels too much like a cat an mouse game to me.

For reference, my implementation that "steals" the KV methods from NSObject:

- (void)addKeyValueCodingImplementation
{
    /* dynamically create a subclass and set it as the class of this mock object */
    Class subclass = OCMCreateSubclass([self mockObjectClass], self);
    object_setClass(self, subclass);

    /* add NSObject's implementation of valueForKey: and valueForKeyPath: to new subclass */
    Method vfkMethod = class_getInstanceMethod([NSObject class], @selector(valueForKey:));
    const char *vfkTypes = method_getTypeEncoding(vfkMethod);
    IMP vfkImp = method_getImplementation(vfkMethod);
    class_addMethod(subclass, @selector(valueForKey:), vfkImp, vfkTypes);

    Method vfkpMethod = class_getInstanceMethod([NSObject class], @selector(valueForKeyPath:));
    const char *vfkpTypes = method_getTypeEncoding(vfkpMethod);
    IMP vfkpImp = method_getImplementation(vfkpMethod);
    class_addMethod(subclass, @selector(valueForKeyPath:), vfkpImp, vfkpTypes);
}

At this point I feel I'm running out of ideas beyond what we discussed in #68. I'm going to close this issue but feel free to re-open it if you have a new idea.