An example of using a matcher pattern in Kiwi message-pattern expectations. See http://stackoverflow.com/questions/15262264/how-to-set-expectations-on-parameters-to-mocked-methods-in-kiwi

SOHaveCountOfGenericMatcher.mm

// A reusable class that satisfies isGenericMatcher:
@interface SOHaveCountOfGenericMatcher : NSObject
- (id)initWithCount:(NSUInteger)count;
- (BOOL)matches:(id)item; // this is what KWMessagePattern looks for
@property (readonly, nonatomic) NSUInteger count;
@end

@implementation SOHaveCountOfGenericMatcher
- (id)initWithCount:(NSUInteger)count
{
    if (self = [super init]) {
        _count = count;
    }
    return self;
}
- (BOOL)matches:(id)item
{
    if (![item respondsToSelector:@selector(count)])
        return NO;
    return [item count] == self.count;
}
@end

// Your spec:
it(@"should receive an array with count 3", ^{
    NSArray* testArray = @[@"a", @"b", @"c"];
    id arrayWithCount3 = [[SOHaveCountOfGenericMatcher alloc] initWithCount:3];
    id aMockObject = [SomeObj nullMock];
    [[[aMockObject should] receive] doSomething:arrayWithCount3];
    [aMockObject doSomething:testArray];
});