MS | Unit Testing Patterns for Asynchronous Networking Communications

A common issue I always run into is how to test asynchronous methods, especially networking calls. I used test the result of the calls, such as the parsing of return data, because testing the entire method proved impossible. I recently read an article from the excellent objc.io publication on asynchronous testing. By combining the patterns used in this article with some refactoring, I finally have my networking code under unit tests.

Here’s what I did:

Architecture

First, I will detail how my app was architected prior to setting up unit tests. I use AFNetworking to handle all API calls, and make use of the AFHTTPClient to centralize all calls to a specific base URL. The HTTPClient would be a singleton, and each service call would be passed a typed return block to execute on completion or failure.

Here is an example for a service call to get a list of items:

In my header:

@interface APIClient : AFHTTPClient

typedef void(^ListItemsRequestReturnBlock)
(BOOL success,NSArray *itemsArray,NSError *error);

-(void)sendItemsRequestForGroupId:(NSNumber *)groupId
completionBlock:(ListItemsRequestReturnBlock)itemsReturnBlock;

@end

And the implementation:

-(void)sendItemsRequestForGroupId:(NSNumber *)groupId
completionBlock:(ListItemsRequestReturnBlock)itemsReturnBlock {
    Group *group = [Group findFirstByAttribute:GroupAttributes.groupID
                                        withValue:groupId];

    NSDictionary *paramsDict = @{
      API_PARAMETER_KEY_ACTION : API_PARAMETER_ACTION_VALUE_ITEMS_REQUEST,
      API_PARAMETER_KEY_GROUP : groupId
    };

    [[SalesCoachAPIClient sharedClient] getPath:nil
                parameters:paramsDict
                success:^(AFHTTPRequestOperation *operation,
                id responseObject) {
					NSArray *lessonClassesArray = nil;
        if ([self checkAPIResponseDictForSuccess:responseObject]) {
            itemsArray = [Item itemsArrayFromAPIDict:responseObject];

            if (itemsArray) {
              [group setItems:[NSSet setWithArray:itemsArray]];
              [[NSManagedObjectContext defaultContext]
              saveToPersistentStoreAndWait];
            }
        }

        if (itemsArray) {
          itemsReturnBlock(YES,itemsArray,nil);
        } else {
          itemsReturnBlock(NO,nil,nil);
        }
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
      itemsReturnBlock(NO,nil,error);
    }];
}

This same pattern is used each time I want to make a call into my API, and a new call is set up for each endpoint. The pattern works well, and has proven itself useful. However, it always felt like the APIClient class was doing a little too much work, and had too much knowledge of the internals of parsing the JSON data returned. This proved to be true once I attempted to apply tests to these methods.

Building the Tests

The first lesson learned: always test and code at the same time (preferably in that order)! This is about the tenth time I have told myself I was too time constrained to write tests while I was coding. In hindsight, it usually means I’ll be doing some heavy refactoring after I start writing tests. The tests always show that the code I wrote quickly is too interdependent, and needs to be broken down more into logical components.

In order to separate concerns and to facilitate mocking data parsing responses, I began to move data parsing code and logic into a separate helper class. This class would be responsible for the following:

Parse the JSON response
Report success ior failure
Create and populate data model objects out of the response
Save the objects to core data
Return core data object(s) from the call after parsing and saving is complete

So with that in mind, the above code changes implementation to look like this:

-(void)sendItemsRequestForGroupId:(NSNumber *)groupId
dataManager:(DataProcessingManager *)dataManager
completionBlock:(ListItemsRequestReturnBlock)itemsReturnBlock {
Group *group = [Group findFirstByAttribute:GroupAttributes.groupID
withValue:groupId];

NSDictionary *paramsDict = @{
  API_PARAMETER_KEY_ACTION: API_PARAMETER_ACTION_VALUE_ITEMS_REQUEST,
  API_PARAMETER_KEY_GROUP: groupId
};

[[APIClient sharedClient] getPath:nil
        parameters:paramsDict
        success:^(AFHTTPRequestOperation *operation, id responseObject) {
          NSArray *itemsArray =
          [dataManager itemsArrayForResponseObject:responseObject];
          if (itemsArray) {
            itemsReturnBlock(YES,lessonClassesArray,nil);
          } else {
            itemsReturnBlock(NO,nil,nil);
          }
        } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
            itemsReturnBlock(NO,nil,error);
        }];
}

This allows me to mock the DataProcessingManager object and tell it what to return. Putting this all together, I now have a way of testing asynchronous API calls with test data and validating that my networking calls are doing the right thing in response to different scenarios.

After this change, one of my tests against this networking call would look like this:

#import <SenTestingKitAsync/SenTestingKitAsync.h>
#import <OCMock/OCMock.h>
#import <OHHTTPStubs/OHHTTPStubs.h>

- (void)testGetItemsRequestSuccessAsync {
  [self setupStubsRequestForResponseName:@"items_request"];
  id manager = [OCMockObject mockForClass:[DataProcessingManager class]];
  NSArray *items = @[@1,@2];
  [[[manager stub] andReturn:items] itemsArrayForResponseObject:OCMOCK_ANY];

  [[SalesCoachAPIClient sharedClient] sendItemsRequestForGroupId:@1
        dataManager:@"ski081"
    completionBlock:^(BOOL success, NSArray *itemsArray, NSError *error) {
       STAssertTrue(success, nil);
       STAssertNil(error, nil);
       STAssertNotNil(itemsArray, nil);
       STAssertTrue(itemsArray.count == 2, nil);
       STSuccess();
    }];
}

I am making use of the following helper methods in my test class:

#pragma mark - Helper
-(OHHTTPStubsResponse *)stubResponseForResponseNamed:(NSString *)responseName
responseTime:(CGFloat)responseTime {
return [OHHTTPStubsResponse responseNamed:responseName
                            fromBundle:self.bundle
                            responseTime:responseTime];
}

-(void)setupStubsRequestForResponseName:(NSString *)responseName {
  OHHTTPStubsResponse *response = [self stubResponseForResponseNamed:responseName
   responseTime:0.1f];
  [OHHTTPStubs stubRequestsPassingTest:^BOOL(NSURLRequest *request) {
    return YES;
  } withStubResponse:^OHHTTPStubsResponse *(NSURLRequest *request) {
    return response;
  }];
}

Final note

To enable testing asynchronous calls, I relied heavilt on the excellent 2nd issue of objc.io. From that article, I was introduced to the OHHTTPStubs and SenTestingKitAsync library.

Some other libraries I am making use of here:

This is a work in progress, but has been the best thing I’ve been able to come up with so far. It definitely relieves some pain for me.

Best of luck testing, and drop me a comment here with any additional tips/suggestions!

Unit Testing Patterns for Asynchronous Networking Communications

Architecture

Building the Tests

Final note

unit-testing