Networking Layer Unit and Integration Testing Techniques using Swift

https://developer.apple.com/videos/play/wwdc2018/417/?time=623

UNIT TESTING : is a level of software testing where individual units components of a software are tested. The purpose is to validate that each unit of the software performs as designed.

INTEGRATION TESTING : is a level of software testing where individual units are combined and tested as a group. The purpose of this level of testing is to expose faults in the interaction between integrated units.

Testing network requests

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Unit Test Request Creation And Parsing

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Integration Testing Network Call

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URLSessionDataTask Integration Testing

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Mocking Using URLProtocol

URLSession provides a high level API for apps to use to perform network requests. Objects like URLSession data tests that represent an inflight request. Behind the scenes though, there’s another lower-level API URLProtocol which performs the underlying work of opening network connection, writing the request, and reading back a response. URLProtocol is designed to be subclassed giving an extensibility point for the URL loading system.

Foundation provides built-in protocols subclasses for common protocols like HTTPS.But we can override these in our tests by providing a mock protocol that lets us make assertions about requests that are coming out and provide mock responses.

URLProtocol communicates progress back to the system via the URLProtocolClient protocol.

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Testing Configuration

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URLSessionDataTask Partial Mocking

Partial mocking, you are modifying an existing type to only partially behave differently in a test

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When you see mock subclasses with overridden method. You are doing Partial mocking
Partial Mocking = Subclasses + Overridden method

Issues with partial Mocking

URLSessionDataTask Complete Mocking

Complete mocking : you are replacing the entire implementation

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