Test block as parameter with OCMock

NetworkManager.h

//
//  NetworkManager.h
//

@import Foundation;

@interface NetworkManager : NSObject

- (void)fetchDataCompletion:(void(^)(NSString *))completion;
- (void)GET:(NSString *)path completion:(void(^)(NSData *))completion;

@end

NetworkManager.m

//
//  NetworkManager.m
//

#import "NetworkManager.h"

@implementation NetworkManager

- (void)fetchDataCompletion:(void(^)(NSString *))completion {
    [self GET:@"/blabla" completion:^(NSData *data) {
        NSString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        completion(string);
    }];
}

- (void)GET:(NSString *)path completion:(void(^)(NSData *))completion {

}

@end

TestMockTests.m

//
//  TestMockTests.m
//

@import XCTest;

#import "NetworkManager.h"

#import <OCMock.h>

@interface TestMockTests : XCTestCase

@end


@implementation TestMockTests

- (void)testExample {
    NetworkManager *manager = [[NetworkManager alloc] init];
    id mockManager = OCMPartialMock(manager);

    NSData *stubData = [@"success" dataUsingEncoding:NSUTF8StringEncoding];
    OCMStub([mockManager GET:@"/blabla" completion:([OCMArg invokeBlockWithArgs:stubData, nil])]);

    XCTestExpectation *expectation = [self expectationWithDescription:@"should be a success"];

    [mockManager fetchDataCompletion:^(NSString *response) {
        XCTAssertEqualObjects(response, @"success");
        [expectation fulfill];
    }];

    [self waitForExpectations:@[expectation] timeout:1];
}

@end