Question

I’m pretty new to TDD and unit testing and I’m giving it a try in a side project.

And I’m kinda stuck in unit testing the dealloc method.

We all know it is a good practice to release custom properties and set them to nil in the dealloc :

-(void) dealloc{
  [myProperty release];
  myProperty = nil;
  [super dealloc];
}

How could I write a unit test that check this behaviour ?

Obviously, this does not work :

[myObject release]
STAssertNil(myObject.myProperty,@"myProperty should be released and set to nil in dealloc")

Any suggestion ?
thanks !

Answer 1

Assuming you could do the above, what would you actually be testing? Here is what i think:

1. testing that -release decrements the retainCount

2. testing that when retainCount reaches zero NSObject’s Garbage Collection mechanism calls -dealloc

3. testing that when -dealloc is called, myProperty is released

This is the wrong granularity for a unit test, points one and two are not your business to test – assume it is unit tested by apple. So, the only bit of the above that is a unit test is:

testing that when -dealloc is called,
myProperty is released

Now, this piece of code (quite rightly) has no logic whatsoever and produces no output. So, i believe that unit testing it is actually paranoid and unnessesary (akin to testing that the compiler actually works).

But if i did want to test it i would do it like so:

OCMockObject *mockProperty = MOCK(NSObject);
[[mockProperty expect] release];
myObject.myProperty = mockProperty;
[myObject dealloc];
[mockProperty verify];

Obviously you should never normally directly call -dealloc, but if you wanted to unit-test -dealloc that is exactly what you should do (or it isn’t a unit-test). Given that this is extremely bad practise and the test gains you very little, i don’t think you should bother.