Stubbing/mocking up webservices for an iOS app

Question

I\'m working on an iOS app whose primary purpose is communication with a set of remote webservices. For integration testing, I\'d like to be able to run my app against some sort

Answer 1

As far as option 1, I have done this in the past using CocoaHTTPServer and embedding the server directly in an OCUnit test:

https://github.com/robbiehanson/CocoaHTTPServer

I put up the code for using this in a unit test here: https://github.com/quellish/UnitTestHTTPServer

After all, HTTP is by design just request/response.

Mocking a web service, wether by creating a mock HTTP server or creating a mock web service in code, is going to be about the same amount of work. If you have X code paths to test, you have at least X code paths to handle in your mock.

For option 2, to mock the web service you would not be communicating with the web service, you would be instead be using the mock object which has known responses. [MyCoolWebService performLogin:username withPassword:password]

would become, in your test

[MyMockWebService performLogin:username withPassword:password] The key point being that MyCoolWebService and MyMockWebService implement the same contract (in objective-c, this would be a Protocol). OCMock has plenty of documentation to get you started.

For an integration test though, you should be testing against the real web service, such as a QA/staging environment. What you are actually describing sounds more like functional testing than integration testing.

Answer 2

OHTTPStubs is a pretty great framework for doing what you want that's gained a lot of traction. From their github readme:

OHTTPStubs is a library designed to stub your network requests very easily. It can help you:

• Test your apps with fake network data (stubbed from file) and simulate slow networks, to check your application behavior in bad network conditions
• Write Unit Tests that use fake network data from your fixtures.

It works with NSURLConnection, new iOS7/OSX.9's NSURLSession, AFNetworking (both 1.x and 2.x), or any networking framework that use Cocoa's URL Loading System.

OHHTTPStubs headers are fully documented using Appledoc-like / Headerdoc-like comments in the header files. You can also read the online documentation here.

Here's an example:

[OHHTTPStubs stubRequestsPassingTest:^BOOL(NSURLRequest *request) {
    return [request.URL.host isEqualToString:@"mywebservice.com"];
} withStubResponse:^OHHTTPStubsResponse*(NSURLRequest *request) {
    // Stub it with our "wsresponse.json" stub file
    NSString* fixture = OHPathForFileInBundle(@"wsresponse.json",nil);
    return [OHHTTPStubsResponse responseWithFileAtPath:fixture
              statusCode:200 headers:@{@"Content-Type":@"text/json"}];
}];

You can find additional usage examples on the wiki page.

Answer 3

You can make a mock web service quite effectively with a NSURLProtocol subclass:

Header:

@interface MyMockWebServiceURLProtocol : NSURLProtocol
@end

Implementation:

@implementation MyMockWebServiceURLProtocol

+ (BOOL)canInitWithRequest:(NSURLRequest *)request
{
    return [[[request URL] scheme] isEqualToString:@"mymock"];
}

+ (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request
{
    return request;
}

+ (BOOL)requestIsCacheEquivalent:(NSURLRequest *)a toRequest:(NSURLRequest *)b
{
    return [[a URL] isEqual:[b URL]];
}

- (void)startLoading
{
    NSURLRequest *request = [self request];
    id <NSURLProtocolClient> client = [self client];
    NSURL *url = request.URL;
    NSString *host = url.host;
    NSString *path = url.path;
    NSString *mockResultPath = nil;
    /* set mockResultPath here … */
    NSString *fileURL = [[NSBundle mainBundle] URLForResource:mockResultPath withExtension:nil];
    [client URLProtocol:self
 wasRedirectedToRequest:[NSURLRequest requestWithURL:fileURL]
       redirectResponse:[[NSURLResponse alloc] initWithURL:url
                                                  MIMEType:@"application/json"
                                     expectedContentLength:0
                                          textEncodingName:nil]];
    [client URLProtocolDidFinishLoading:self];
}

- (void)stopLoading
{
}

@end

The interesting routine is -startLoading, in which you should process the request and locate the static file corresponding to the response in the app bundle before redirecting the client to that file URL.

You install the protocol with

[NSURLProtocol registerClass:[MyMockWebServiceURLProtocol class]];

And reference it with URLs like

mymock://mockhost/mockpath?mockquery

This is considerably simpler than implementing a real webservice either on a remote machine or locally within the app; the tradeoff is that simulating HTTP response headers is much more difficult.

Answer 4

I'd suggest to use Nocilla. Nocilla is a library for stubbing HTTP requests with a simple DSL.

Let's say that you want to return a 404 from google.com. All you have to do is:

stubRequest(@"GET", "http://www.google.com").andReturn(404); // Yes, it's ObjC

After that, any HTTP to google.com will return a 404.

A more complete example, where you want to match a POST with a certain body and headers and return a canned response:

stubRequest(@"POST", @"https://api.example.com/dogs.json").
withHeaders(@{@"Accept": @"application/json", @"X-CUSTOM-HEADER": @"abcf2fbc6abgf"}).
withBody(@"{\"name\":\"foo\"}").
andReturn(201).
withHeaders(@{@"Content-Type": @"application/json"}).
withBody(@"{\"ok\":true}");

You can match any request and fake any response. Check the README for more details.

The benefits of using Nocilla over other solutions are:

• It's fast. No HTTP servers to run. Your tests will run really fast.
• No crazy dependencies to manage. On top of that, you can use CocoaPods.
• It's well tested.
• Great DSL that will make your code really easy to understand and maintain.

The main limitation is that it only works with HTTP frameworks built on top of NSURLConnection, like AFNetworking, MKNetworkKit or plain NSURLConnection.

Hope this helps. If you need anything else, I'm here to help.

Answer 5

I am assuming you are using Objective-C. For Objective-C OCMock is widely used for mocking/unit testing (your second option).

I used OCMock for the last time more than a year ago, but as far as I remember it is a fully-fledged mocking framework and can do all the things that are described below.

One important thing about mocks is that you can use as much or as little of the actual functionality of your objects. You can create an 'empty' mock (which will have all the methods is your object, but will do nothing) and override just the methods you need in your test. This is usually done when testing other objects that rely on the mock.

Or you can create a mock that will act as your real object behaves, and stub out some methods that you do not want to test at that level (e.g. - methods that actually access the database, require network connection, etc.). This is usually done when you are testing the mocked object itself.

It is important to understand that you do not create mocks once and for all. Every test can create mocks for the same objects anew based on what is being tested.

Another important thing about mocks is that you can 'record' scenarious (sequences of calls) and your 'expectations' about them (which methods behind the scenes should be called, with which parameters, and in which order), then 'replay' the scenario - the test will fail if the expectations were not met. This is the main difference between classical and mockist TDD. It has its pros and cons (see Martin Fowler's article).

Let's now consider your specific example (I'll be using pseudo-syntax that looks more like C++ or Java rather than Objective C):

Let's say you have an object of class LoginForm that represents the login information entered. It has (among others) methods setName(String),setPassword(String), bool authenticateUser(), and Authenticator* getAuthenticator().

You also have an object of class Authenticator which has (among others) methods bool isRegistered(String user), bool authenticate(String user, String password), and bool isAuthenticated(String user).

Here's how you can test some simple scenarios:

Create MockLoginForm mock with all methods empty except for the four mentioned above. The first three methods will be using actual LoginForm implementation; getAuthenticator() will be stubbed out to return MockAuthenticator.

Create MockAuthenticator mock that will use some fake database (such as an internal data structure or a file) to implement its three methods. The database will contain only one tuple: ('rightuser','rightpassword').

TestUserNotRegistered

Replay scenario:

MockLoginForm.setName('wronuser');
MockLoginForm.setPassword('foo');
MockLoginForm.authenticate();

Expectations:

getAuthenticator() is called
MockAuthenticator.isRegistered('wrognuser') is called and returns 'false'

TestWrongPassword

Replay scenario:

MockLoginForm.setName('rightuser');
MockLoginForm.setPassword('foo');
MockLoginForm.authenticate();

Expectations:

getAuthenticator() is called
MockAuthenticator.isRegistered('rightuser') is called and returns 'true'
MockAuthenticator.authenticate('rightuser','foo') is called and returns 'false'

TestLoginOk

Replay scenario:

MockLoginForm.setName('rightuser');
MockLoginForm.setPassword('rightpassword');
MockLoginForm.authenticate();
result = MockAuthenticator.isAuthenticated('rightuser')

Expectations:

getAuthenticator() is called
MockAuthenticator.isRegistered('rightuser') is called and returns 'true'
MockAuthenticator.authenticate('rightuser','rightpassword') is called and returns 'true'
result is 'true'

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I hope this helps.