Unit testing a method that relies on an NSMapTable to clean up objects that lack strong references - objective-c

Question

So I have the following method (it's an UIView category method to supplement nib loading, however, it has been cleaned up to be more relevant here):
+ (id) loadFromNib {
NSString* nibName = NSStringFromClass([self class]);
NSArray* elements = [[NSBundle mainBundle] loadNibNamed:nibName owner:nil options:nil];
NSMutableArray* foundCustomObjects = [NSMutableArray array];
NSObject* foundViewObject = nil;
for (NSObject* anObject in elements) {
if ([anObject isKindOfClass:[self class]] && foundViewObject == nil) {
foundViewObject = anObject;
// Keep strong references to non-UIView custom objects (to prevent them from being released due to having weak-only references):
} else if (![anObject isKindOfClass:[UIView class]]) {
[foundCustomObjects addObject:anObject];
}
}
// Generate strong references to all found custom objects:
if (foundViewObject != nil) {
[foundCustomObjects enumerateObjectsUsingBlock:
^(id obj, NSUInteger idx, BOOL *stop) {
[customObjects setObject:foundViewObject forKey:obj];
// (Yes, I will skip objects that are strongly referenced by their view later on)
}];
}
return foundViewObject;
}
And customObjects is a static variable defined as:
+ (void) initialize {
if (customObjects == nil) {
// For each view that holds a custom object, store a strong reference to that object here, that way preventing the object from being deallocated due to weak referencing (in UICollectionView.delegate, for example):
customObjects = [NSMapTable mapTableWithKeyOptions:NSMapTableStrongMemory valueOptions:NSMapTableWeakMemory];
}
}
My problem is that I want to unit test the fact that deallocated views really result in deallocating the referenced "custom object". How should I do that?
This is what I've got so far (using OCMock):
- (void) test {
/*
* SETUP */
NSObject* __weak weakRefToSomeObject;
UIView* someView;
NSObject* someObject;
#autoreleasepool {
someView = [[UIView alloc] init];
someObject = [[NSObject alloc] init];
NSArray* nibElements = #[someView, someObject];
id mainBundleMock = [OCMockObject niceMockForClass:[NSBundle class]];
[[[mainBundleMock stub] andReturn:nibElements] loadNibNamed:[OCMArg any] owner:[OCMArg any] options:[OCMArg any]];
id NSBundleMock = [OCMockObject niceMockForClass:[NSBundle class]];
[[[NSBundleMock stub] andReturn:mainBundleMock] mainBundle];
/*
* RUN */
weakRefToSomeObject = someObject;
[UIView loadFromNib];
someObject = nil;
nibElements = nil;
[mainBundleMock stopMocking];
[NSBundleMock stopMocking];
mainBundleMock = nil;
NSBundleMock = nil;
}
/*
* VERIFY */
XCTAssertNotNil(weakRefToSomeObject); // This passes!
#autoreleasepool {
someView = nil;
}
XCTAssertNil(weakRefToSomeObject); // This does not pass - why?
}
At the last row, I expect the key-value pair (where the view was referenced weakly) to be dropped, that way dropping the last strong reference to someObject, and thus rendering weakRefToSomeObject nil.
I have also tried to add someView = nil to the first autoreleasepool (just below NSBundleMock = nil), but that didn't help.
Any ideas?

Answer 1

I fixed this by adding an access function:
// Allow tests to access the customObjects map:
NSMapTable* getCustomObjectsMap() {
return customObjects;
}
And then declaring it in my unit test document:
// Declare method that gives us access to the static customObjects variable:
NSMapTable* getCustomObjectsMap();
Thus the test code ended up to be:
- (void) testCustomObjectLifecycleFromStartToFinish {
/*
* ASSERT REQUIRED INITIAL STATE */
XCTAssertNil([[getCustomObjectsMap() objectEnumerator] nextObject]);
/*
* SETUP */
UIView* someView = [[UIView alloc] init];
NSObject* someObject = [[NSObject alloc] init];
#autoreleasepool {
#autoreleasepool {
NSArray* nibElements = #[someView, someObject];
id mainBundleMock = [OCMockObject niceMockForClass:[NSBundle class]];
[[[mainBundleMock stub] andReturn:nibElements] loadNibNamed:[OCMArg any] owner:[OCMArg any] options:[OCMArg any]];
id NSBundleMock = [OCMockObject niceMockForClass:[NSBundle class]];
[[[NSBundleMock stub] andReturn:mainBundleMock] mainBundle];
/*
* RUN */
[UIView loadFromNib];
someObject = nil;
nibElements = nil;
}
/*
* VERIFY */
XCTAssertNotNil([[getCustomObjectsMap() objectEnumerator] nextObject]);
// Dropping last strong reference to view:
someView = nil;
}
// Without strong references to someView, the objects map should have been emptied:
XCTAssertNil([[getCustomObjectsMap() objectEnumerator] nextObject]);
}