Fake It ‘Til You Make It: Staying Productive when Working with Web Services

Most apps we build are backed by some form of API. When these APIs are pre-existing or bug free, great! What happens when another team is building the API while you are building the app? How can you build a view with data that doesn’t actually exist? We will review some options for staying productive when working with external teams by exploring:

* Best practices for API development with external teams
* Options for testing nonexistent APIs
* Foundation’s URL Loading System to fake API requests that are in development

Transcript

1. Fake It ’Til You Make It
   Staying Productive when Working with Web
   Services
   Josh Johnson | @jnjosh | jnjosh.com
   

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2. Most Apps Require Web Services
   

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3. “My API is perfect and has no bugs!”
   — A really lucky person
   

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4. “Welcome to the Real World”
   — Morpheus
   

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5. You still need to make progress!
   What can you do?
   

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7. Dummy Data
   

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8. Build it as if
   you have the API
   

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9. Agree on an API spec
   

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10. Wait? There is no API.
    How can we build it?
    

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11. Build your own lightweight API
    

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12. Sinatra
    Using tools like Sinatra you can quickly define API endpoints to
    match tha API spec
    get '/episodes/:episode' do
    last_modified episodes.first[:published]
    content_type :json
    episodes.select { |e| e[:number] == params[:episode].to_i }.to_json
    end
    㱺 GET http://api.testing.com/episodes/8
    

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13. The Do it Yourself API
    

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14. Dummy Data
    +
    The Do it Yourself API
    

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15. NSURLProtocol
    and the
    URL Loading System
    

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16. How does NSURLProtocol help us?
    

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17. Let's download an image!
    NSString *kittenImageString = @"http://cutekittenimages.com/kittens_cute_kitten.jpg";
    NSURL *url = [NSURL URLWithString:kittenImageString];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request addValue:@"image/jpeg" forHTTPHeaderField:@"Content-Type"];
    [NSURLConnection sendAsynchronousRequest:request queue:self.imageQueue completionHandler:
    ^(NSURLResponse *response, NSData *data, NSError *connectionError) {
    UIImage *kittenImage = [UIImage imageWithData:data scale:0.0];
    [[NSOperationQueue mainQueue] addOperation:[NSBlockOperation blockOperationWithBlock:^{
    self.imageView.image = kittenImage;
    }]];
    }];
    

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19. Introducing TWTHasslehoffImageProtocol
    @import Foundation;
    @interface TWTHasselhoffImageProtocol : NSURLProtocol
    @end
    

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20. Register the Hasselhoff Protocol
    - (BOOL)application:(UIApplication *)application
    didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
    {
    [NSURLProtocol registerClass:[TWTHasselhoffImageProtocol class]];
    return YES;
    }
    

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21. Implement the Hasselhoff Image Protocol
    + (BOOL)canInitWithRequest:(NSURLRequest *)request
    {
    NSSet *validContentTypes = [NSSet setWithArray:@[ @"image/png",
    @"image/jpg",
    @"image/jpeg" ]];
    return [validContentTypes containsObject:request.allHTTPHeaderFields[@"Content-Type"]];
    }
    + (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request
    {
    return request;
    }
    

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22. Implement the Hasselhoff Image Protocol
    - (void)startLoading
    {
    id client = self.client;
    NSURLRequest *request = self.request;
    NSDictionary *headers = @{ @"Content-Type": @"image/jpeg" };
    NSData *imageData = UIImageJPEGRepresentation([UIImage imageNamed:@"David_Hasselhoff.jpeg"], 1.0);
    NSHTTPURLResponse *response = [[NSHTTPURLResponse alloc] initWithURL:request.URL
    statusCode:200
    HTTPVersion:@"HTTP/1.1"
    headerFields:headers];
    [client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed];
    [client URLProtocol:self didLoadData:imageData];
    [client URLProtocolDidFinishLoading:self];
    }
    - (void)stopLoading
    {
    // Must be implemented
    }
    

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24. This is great and all, but it is a canned example.
    

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25. HolyMockURL, it's URLMock
    https://github.com/twotoasters/URLMock
    

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26. Let's check the weather!
    - (NSOperation *)fetchTemperatureForLatitude:(NSNumber *)latitude
    longitude:(NSNumber *)longitude
    success:(void (^)(NSNumber *))successBlock
    failure:(void (^)(NSError *))failureBlock
    {
    NSParameterAssert(latitude && ABS(latitude.doubleValue) <= 90.0);
    NSParameterAssert(longitude && ABS(longitude.doubleValue) <= 180.0);
    return [self.operationManager GET:@"weather"
    parameters:@{ @"lat" : latitude, @"lon" : longitude }
    success:^(AFHTTPRequestOperation *operation, id response) {
    if (successBlock) {
    successBlock([response valueForKeyPath:@"main.temp"]);
    }
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    if (failureBlock) {
    failureBlock(error);
    }
    }];
    }
    

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27. A pretty bad unit test
    - (void)testFetchTemperatureForLatitudeLongitude
    {
    __block NSNumber *temperature = nil;
    [self.APIClient fetchTemperatureForLatitude:@(35.99)
    longitude:@(-78.9)
    success:^(NSNumber *kelvins) {
    temperature = kelvins;
    }
    failure:nil];
    // Assert that temperature != nil before 2.0s elapse
    UMKAssertTrueBeforeTimeout(2.0, temperature != nil, @"temperature isn't set in time");
    }
    

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28. Let's use URLMock
    + (void)setUp
    {
    [super setUp];
    [UMKMockURLProtocol enable];
    [UMKMockURLProtocol setVerificationEnabled:YES];
    }
    + (void)tearDown
    {
    [UMKMockURLProtocol setVerificationEnabled:NO];
    [UMKMockURLProtocol disable];
    [super tearDown];
    }
    - (void)setUp
    {
    [super setUp];
    [UMKMockURLProtocol reset];
    …
    }
    

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29. A better unit test, with URLMock
    - (void)testFetchTemperatureForLatitudeLongitudeCorrectData
    {
    // setting up latitude, longitude and tempearture to expect
    NSURL *temperatureURL = [self temperatureURLWithLatitude:latitude longitude:longitude];
    [UMKMockURLProtocol expectMockHTTPGetRequestWithURL:temperatureURL
    responseStatusCode:200
    responseJSON:@{ @"main" : @{ @"temp" : temperature } }];
    __block BOOL succeeded = NO;
    __block BOOL failed = NO;
    __block NSNumber *kelvins = nil;
    [self.APIClient fetchTemperatureForLatitude:latitude
    longitude:longitude
    success:^(NSNumber *temperatureInKelvins) {
    succeeded = YES;
    kelvins = temperatureInKelvins;
    }
    failure:^(NSError *error) {
    failed = YES;
    }];
    UMKAssertTrueBeforeTimeout(1.0, succeeded, @"success block is not called");
    UMKAssertTrueBeforeTimeout(1.0, !failed, @"failure block is called");
    UMKAssertTrueBeforeTimeout(1.0, [kelvins isEqualToNumber:temperature], @"incorrect temperature");
    NSError *verificationError = nil;
    XCTAssertTrue([UMKMockURLProtocol verifyWithError:&verificationError], @"verification failed");
    }
    

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30. Test for errors, with URLMock
    - (void)testFetchTemperatureForLatitudeLongitudeError
    {
    …
    NSURL *temperatureURL = [self temperatureURLWithLatitude:latitude longitude:longitude];
    [UMKMockURLProtocol expectMockHTTPGetRequestWithURL:temperatureURL responseError:[self randomError]];
    __block BOOL succeeded = NO;
    __block BOOL failed = NO;
    [self.APIClient fetchTemperatureForLatitude:latitude
    longitude:longitude
    success:^(NSNumber *temperature) {
    succeeded = YES;
    }
    failure:^(NSError *error) {
    failed = YES;
    }];
    UMKAssertTrueBeforeTimeout(1.0, !succeeded, @"success block is called");
    UMKAssertTrueBeforeTimeout(1.0, failed, @"failure block is not called");
    NSError *verificationError = nil;
    XCTAssertTrue([UMKMockURLProtocol verifyWithError:&verificationError], @"verification failed");
    }
    

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31. URLMock
    https://github.com/twotoasters/URLMock
    

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32. Working with a Web Service is a pain.
    

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33. Thank you! Questions?
    Josh Johnson | @jnjosh | jnjosh.com
    https://github.com/twotoasters/URLMock
    https://objectivetoast.com
    

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