Completion Blocks in Cedar

Backgrounder.h

typedef void(^BackgroundCompletion)();

@interface Backgrounder : NSObject
- (void)executeInBackground:(BackgroundCompletion)completion;
@end

Spec.mm

describe(@"when the backgrounder completes", ^{
    __block Backgrounder *backgrounder;
    __block BackgroundCompletion completion;

    beforeEach(^{
        backgrounder = nice_fake_for([Backgrounder class]);

        completion = nil;
        backgrounder stub_method(@selector(executeInBackground:))
        .and_do_block(^(BackgroundCompletion localCompletion) {
            completion = localCompletion;
        });

        // call this whenever you want
        completion();
    });
});