Testable Network Layer in Swift – Part 3

Mocking URLProtocol

Please check the previous articles on Network Layer Part 1 and Part 2.

Mocking URLProtocol

What is Mocking?

In object-oriented programming, mock objects are simulated objects that mimic the behavior of real objects in controlled ways. (source: wiki)

In our case, we are looking to mimic a URLSession so that it will return the mock object without hitting the physical server. We can achieve this by creating MockURLProtocol that conforms to URLProtocol and implements its required methods. Now our MockURLProtocol will be capable of handling the specified request.

Testable Network Layer


Now we need to add our MockURLProtocol to the URLSessionConfiguration.protocolClasses array to handle requests in a session.

Testable Network Layer

Custom URLSessionConfiguration

Mocking in Action:

For example, when mocking the loginUser function, we will prepare a fake response object that mimics what we expect on a real server call. This response object will be returned as a response from the requestHandler of the MockURLProtocol.


Actual implementation for reference


Testable Network Layer in Swift

Fake response object


The final mockLoginUser function will look like this:

Testable Network Layer

Mock loginUser function


Now check the APIMockingTests.swift file in the sample code.

Then check updates in the APIHandler.swift file, as updated code using Builder Pattern and refactored BaseRequest, AuthRequest with RequestBuilder.

Run the tests again. After refactoring the code, we observed that all the tests passed without changing the test cases. The advantage of testing is that we can guarantee that all cases are handled even after refactoring.

You can find the complete source code below:

To share files related to blogs which can be made public — appitventures/IOS-Bloggithub.com

This is based on WWDC 2018: “Testing Tips & Tricks”

link: https://developer.apple.com/videos/play/wwdc2018/417/

Download Your Free Mobile App Development eBook


Subscribe to our newsletter!