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URLMock is an Objective-C framework for mocking and stubbing URL requests and responses. It works with APIs built on the Foundation NSURL loading system—NSURLConnection, NSURLSession, and AFNetworking, for example—with almost no changes to your code.


  • Simple, well-documented Objective-C API
  • Minimal setup necessary
  • Works with APIs built atop the Foundation NSURL loading system
  • Designed with both response stubbing and unit testing in mind
  • Can be used for some or all of your project’s URL requests
  • Well-tested and includes lots of helpful testing utilities
  • Works on macOS, iOS, and tvOS

What’s New in URLMock 1.3.6

URLMock 1.3.6 adds support for installing using Swift Package Manager.


The easiest way to start using URLMock is to install it with CocoaPods.

pod 'URLMock'

Installing Subspecs

URLMock has two CocoaPods subspecs, TestHelpers and SubclassResponsibility. TestHelpers includes a wide variety of useful testing functions. See UMKTestUtilities.h for more details. It can be installed by adding the following line to your Podfile:

pod 'URLMock/TestHelpers'

Similarly, the SubclassResponsibility subspec can be installed by adding the following line to your Podfile:

pod 'URLMock/SubclassResponsibility'

This subspec adds methods to NSException to easily raise exceptions in methods for which subclasses must provide an implementation. See NSException+UMKSubclassResponsibility.h for details.

Using URLMock

URLMock is designed with both response stubbing and unit testing in mind. Both work very similarly.

Response stubbing

Using URLMock for response stubbing is simple:

First, enable URLMock.

[UMKMockURLProtocol enable];

If you are using NSURLSession and not using the shared session, you also need to add UMKMockURLProtocol to your session configuration’s set of allowed protocol classes.

NSURLSessionConfiguration *configuration = …;
configuration.protocolClasses = @[ [UMKMockURLProtocol class] ];
NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration];

Next, add an expected mock request and response.

// The request is a POST with some JSON data
NSURL *URL = [NSURL URLWithString:@""];
id requestJSON = @{ @"person" : @{ @"name" : @"John Doe",
                                   @"age" : @47 } };
id responseJSON = @{ @"person" : @{ @"id" : @1,
                                    @"name" : @"John Doe",
                                    @"age" : @47 } };

[UMKMockURLProtocol expectMockHTTPPostRequestWithURL:URL

Mock requests and responses are not limited to having JSON bodies; they can also have bodies with strings, WWW form-encoded parameter dictionaries, or arbitrary NSData instances. There are also mock responders for responding with an error or returning data in chunks with a delay between each chunk, and we’ll be adding more responders in the future.

When you execute your real request, you will get the stubbed response back. You don’t have to make any changes to your code when using URLMock. Things should just work. For example, the following URLConnection code will receive the mock response above:

NSURL *URL = [NSURL URLWithString:@""];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:URL];
request.HTTPMethod = @"POST";
id bodyJSON = @{ @"person" : @{ @"name" : @"John Doe", @"age" : @47 } };
request.HTTPBody = [NSJSONSerialization dataWithJSONObject:bodyJSON

// Create the connection as usual
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:…];

The following AFNetworking code would accomplish the same thing:

NSURL *base = [NSURL URLWithString:@""];
id params = @{ @"person" : @{ @"name" : @"John Doe", @"age" : @47 } };

// Send a POST as usual
AFHTTPRequestOperationManager *om = [[AFHTTPRequestOperationManager alloc] initWithBaseURL:base];
om.requestSerializer = [AFJSONRequestSerializer serializer];
[om POST:@"person" parameters:params success:^(AFHTTPRequestOperation *op, id object) {
} failure:^(AFHTTPRequestOperation *op, NSError *error) {

Pattern-Matching Mock Requests

You can also create a mock request that responds dynamically to the request it matches against using UMKPatternMatchingMockRequest. To create a pattern-matching mock request, you need to provide a URL pattern, e.g., @"". When a URL request matches this pattern, the mock request generates an appropriate responder using its responder generation block:

NSString *pattern = @"";
UMKPatternMatchingMockRequest *mockRequest =  [[UMKPatternMatchingMockRequest alloc] initWithPattern:pattern];
mockRequest.HTTPMethods = [NSSet setWithObject:kUMKMockHTTPRequestPostMethod];

mockRequest.responderGenerationBlock = ^id<UMKMockURLResponder>(NSURLRequest *request, NSDictionary *parameters) {
    NSDictionary *requestJSON = [request umk_JSONObjectFromHTTPBody];

    // Respond with
    //   {
    //     "follower_id": «New follower’s ID»,
    //     "following_id":  «Account ID that was POSTed to»
    //   }
    UMKMockHTTPResponder *responder = [UMKMockHTTPResponder mockHTTPResponderWithStatusCode:200];
    [responder setBodyWithJSONObject:@{ @"follower_id" : requestJSON[@"follower_id"],
                                        @"following_id" : @([parameters[@"accountID"] integerValue]) }];
    return responder;

[UMKMockURLProtocol addExpectedMockRequest:mockRequest];

See the documentation for UMKPatternMatchingMockRequest for more information.

Unit testing

Unit testing with URLMock is very similar to response stubbing, but you can use a few additional APIs to make unit testing easier.

First, enable verification in UMKMockURLProtocol using +setVerificationEnabled:. This enables tracking whether any unexpected requests were received. It makes sense to do this in your XCTestCase’s +setUp method. You can also disable verification in your +tearDown method.

+ (void)setUp
    [super setUp];
    [UMKMockURLProtocol enable];
    [UMKMockURLProtocol setVerificationEnabled:YES];

+ (void)tearDown
    [UMKMockURLProtocol setVerificationEnabled:NO];
    [UMKMockURLProtocol disable];
    [super tearDown];

Before (or after) each test, invoke +[UMKMockURLProtocol reset]. This resets UMKMockURLProtocol’s expectations to their original state. It does not change whether verification is enabled.

If you’re using XCTest, the ideal place to do this is in your test case’s ‑setUp (or ‑tearDown) method.

- (void)setUp
   [super setUp];
   [UMKMockURLProtocol reset];

After you’ve executed the code you’re testing, send UMKMockURLProtocol the +verifyWithError: message. It will return YES if all expected mock requests were serviced and no unexpected mock requests were received.

NSError *error = nil;
XCTAssertTrue([UMKMockURLProtocol verifyWithError:&error], @"…");

For the strictest testing, enable header checking on your UMKMockHTTPRequest instances. When enabled, mock requests only match URL requests that have equivalent headers. You can enable header checking on mock HTTP request by setting its checksHeadersWhenMatching property to YES or by using ‑initWithHTTPMethod:URL:checksHeadersWhenMatching:.

UMKMockHTTPRequest *request = [UMKMockHTTPRequest mockHTTPGetRequestWithURL:URL];
request.checksHeadersWhenMatching = YES;

Note that some networking APIs—most notably AFNetworking—send headers that you didn’t explicitly set, so you should determine what those are before creating your mock requests. To make things a little easier, you can use +[UMKMockHTTPRequest setDefaultHeaders:] to set the default headers for new UMKMockHTTPRequest instances. For example, if you’re using AFNetworking’s default HTTP request serializer, you can set default headers this way:

[UMKMockHTTPRequest setDefaultHeaders:[[AFHTTPRequestSerializer serializer] HTTPRequestHeaders]];

Non-HTTP Protocols

Out of the box, URLMock only supports HTTP and HTTPS. However, it is designed to work with any URL protocol that the NSURL loading system can support. If you are using a custom scheme or URL protocol and would like to add support for mocking requests and responses, you need only create classes that conform to the UMKMockURLRequest and UMKMockURLResponder protocols. See the implementations of UMKMockHTTPRequest and UMKMockHTTPResponder for examples.


@jnjosh, @prachigauriar, @macdrevx, and @dfowj currently act as the owners of URLMock. Mention us in issues or pull requests for questions about features, project direction, or to request code review.

Contributing, Filing Bugs, and Requesting Enhancements

URLMock is very usable in its current state, but there’s still a lot that could be done. If you would like to help fix bugs or add features, send us a pull request!

We use GitHub issues for bugs, enhancement requests, and the limited support we provide, so open an issue for any of those.

Typically, a pull request should receive a code review and a 👍 from at least 2 project owners before being merged. In cases where a pull request review needs to be expedited a single 👍 from an owner will suffice, though this should be the exception, not the rule.


All code is licensed under the MIT license. Do with it as you will.


A Cocoa framework for mocking and stubbing URL requests and responses.




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