how to unit test a NSURLConnection Delegate?

Question

How can I unit test my NSURLConnection delegate? I made a ConnectionDelegate class which conforms to different protocols to serve data from the web to different ViewControllers. Before I get too far I want to start writing my unit tests. But I don't know how to test them as a unit without the internet connection. I would like also what I should do to treat the asynchronous callbacks.

Answer 1

This is similar to Jon's response, couldn't fit it into a comment, though. The first step is to make sure you are not creating a real connection. The easiest way to achieve this is to pull the creation of the connection into a factory method and then substitute the factory method in your test. With OCMock's partial mock support this could look like this.

In your real class:

- (NSURLConnection *)newAsynchronousRequest:(NSURLRequest *)request
{
    return [[NSURLConnection alloc] initWithRequest:request delegate:self];
}

In your test:

id objectUnderTest = /* create your object */
id partialMock = [OCMockObject partialMockForObject:objectUnderTest];
NSURLConnection *dummyUrlConnection = [[NSURLConnection alloc] 
    initWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"file:foo"]] 
    delegate:nil startImmediately:NO];
[[[partialMock stub] andReturn:dummyUrlConnection] newAsynchronousRequest:[OCMArg any]];

Now, when your object under test tries to create the URL connection it actually gets the dummy connection created in the test. The dummy connection doesn't have to be valid, because we're not starting it and it never gets used. If your code does use the connection you could return another mock, one that mocks NSURLConnection.

The second step is to invoke the method on your object that triggers the creation of the NSURLConnection:

[objectUnderTest doRequest];

Because the object under test is not using the real connection we can now call the delegate methods from the test. For the NSURLResponse we're using another mock, the response data is created from a string that's defined somewhere else in the test:

int statusCode = 200;
id responseMock = [OCMockObject mockForClass:[NSHTTPURLResponse class]];
[[[responseMock stub] andReturnValue:OCMOCK_VALUE(statusCode)] statusCode];
[objectUnderTest connection:dummyUrlConnection didReceiveResponse:responseMock];

NSData *responseData = [RESPONSE_TEXT dataUsingEncoding:NSASCIIStringEncoding];
[objectUnderTest connection:dummyUrlConnection didReceiveData:responseData];

[objectUnderTest connectionDidFinishLoading:dummyUrlConnection];

That's it. You've effectively faked all the interactions the object under test has with the connection, and now you can check whether it is in the state it should be in.

If you want to see some "real" code, have a look at the tests for a class from the CCMenu project that uses NSURLConnections. This is a little bit confusing because the class that's tested is named connection, too.

http://ccmenu.svn.sourceforge.net/viewvc/ccmenu/trunk/CCMenuTests/Classes/CCMConnectionTest.m?revision=129&view=markup

Answer 2

EDIT (2-18-2014): I just stumbled across this article with a more elegant solution.

http://www.infinite-loop.dk/blog/2011/04/unittesting-asynchronous-network-access/

Essentially, you have the following method:

- (BOOL)waitForCompletion:(NSTimeInterval)timeoutSecs {
    NSDate *timeoutDate = [NSDate dateWithTimeIntervalSinceNow:timeoutSecs];

    do {
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:timeoutDate];
        if([timeoutDate timeIntervalSinceNow] < 0.0)
            break;
    } while (!done);

    return done;
}

At the end of your test method, you make sure things haven't timed out:

STAssertTrue([self waitForCompletion:5.0], @"Timeout");

Basic format:

- (void)testAsync
{
    // 1. Call method which executes something asynchronously 
    [obj doAsyncOnSuccess:^(id result) {
        STAssertNotNil(result);
        done = YES;
    }
    onError:^(NSError *error) [
        STFail();
        done = YES;
    }

    // 2. Determine timeout
    STAssertTrue([self waitForCompletion:5.0], @"Timeout");
}    

==============

I'm late to the party, but I came across a very simple solution. (Many thanks to http://www.cocoabuilder.com/archive/xcode/247124-asynchronous-unit-testing.html)

.h file:

@property (nonatomic) BOOL isDone;

.m file:

- (void)testAsynchronousMethod
{
    // 1. call method which executes something asynchronously.

    // 2. let the run loop do its thing and wait until self.isDone == YES
    self.isDone = NO;
    NSDate *untilDate;
    while (!self.isDone)
    {
        untilDate = [NSDate dateWithTimeIntervalSinceNow:1.0]
        [[NSRunLoop currentRunLoop] runUntilDate:untilDate];
        NSLog(@"Polling...");
    }

    // 3. test what you want to test
}

isDone is set to YES in the thread that the asynchronous method is executing.

So in this case, I created and started the NSURLConnection at step 1 and made the delegate of it this test class. In

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response

I set self.isDone = YES;. We break out of the while loop and the test is executed. Done.

Answer 3

I avoid networking in unit tests. Instead:

• I isolate NSURLConnection within a method.
• I create a testing subclass, overriding that method to remove all traces of NSURLConnection.
• I write one test to ensure that the method in question will get invoked when I want. Then I know it'll fire off an NSURLConnection in real life.

Then I concentrate on the more interesting part: Synthesize mock NSURLResponses with various characteristics, and pass them to the NSURLConnectionDelegate methods.