Meta alert: A Kiwi matcher that allows you to define custom matchers with one block instead of subclassing KWMatcher.

gistfile1.m

#import "KWMatcher.h"

typedef BOOL (^FTKiwiCustomMatcherBlock)(id subject);

@interface FTKiwiCustomBlockMatcher : KWMatcher

// Your custom matcher block will receive the expectation ‘subject’ and must
// return `YES` if the expaction passes or `NO` if it fails.
- (void)be:(FTKiwiCustomMatcherBlock)block;

@end

gistfile2.m

#import "FTKiwiCustomBlockMatcher.h"

@interface FTKiwiCustomBlockMatcher ()
@property (copy) FTKiwiCustomMatcherBlock customMatcherBlock;
@end

@implementation FTKiwiCustomBlockMatcher

@synthesize customMatcherBlock = _customMatcherBlock;

// Enable this if you’re not using ARC.
//
//- (void)dealloc {
  //Block_release(_customMatcherBlock);
  //[super dealloc];
//}

+ (NSArray *)matcherStrings {
    return @[@"be:"];
}

- (BOOL)evaluate {
    return self.customMatcherBlock(self.subject);
}

- (NSString *)failureMessageForShould {
    return @"expected the customer matcher to evaluate to `YES`";
}

- (NSString *)failureMessageForShouldNot {
    return @"expected the customer matcher to evaluate to `NO`";
}

- (void)be:(FTKiwiCustomMatcherBlock)block {
    self.customMatcherBlock = block;
}

@end

gistfile3.m

#import "Kiwi.h"
#import "FTKiwiCustomBlockMatcher.h"

typedef FTKiwiCustomMatcherBlock (^StringWithContentMatcher)(NSString *content);

SPEC_BEGIN(ExampleSpec)

registerMatchers(@"FT");

describe(@"FTKiwiCustomBlockMatcher", ^{
  it(@"takes a block that does the actual evaluation", ^{
    FTKiwiCustomMatcherBlock stringInstance = ^(id subject) {
      return [subject isKindOfClass:[NSString class]];
    };

    [[@"hello, I am string" should] be:stringInstance];
  });

  it(@"becomes even more interesting with dynamic arguments", ^{
    StringWithContentMatcher stringWithContent = ^(NSString *content) {
      return ^(id subject) {
        return [subject isKindOfClass:[NSString class]] && [subject isEqualToString:content];
      };
    };

    [[@"hello, I am string" should] be:stringWithContent(@"hello, I am string")];
  });
});

SPEC_END