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Testing Strategies - iOS

Best Practices for Unit Testing ViewControllers

Hey everyone,

I'm looking to refine our unit testing approach for ViewControllers in our iOS applications. We're currently using XCTest, but I feel there are areas we can improve, especially around mocking dependencies and asserting UI states.

What are your favorite strategies for:

  • Mocking networking calls and data managers?
  • Testing user interactions and navigation flows?
  • Asserting dynamic UI elements and states?

Any insights or favorite libraries would be greatly appreciated!

Great question, Jane!

For mocking dependencies, we've found dependency injection to be key. By injecting mock objects into our ViewControllers during tests, we can isolate them effectively. Libraries like OHHTTPStubs are fantastic for stubbing network requests.

For UI testing, consider using XCUITest for end-to-end flows, but for unit tests, focusing on the ViewModel or Presenter logic is often more efficient. If you must test ViewController UI directly, libraries like SnapshotTesting can be a lifesaver for visual regression.

Echoing Mike's point on dependency injection. We use a protocol-oriented approach extensively. For example, instead of a `NetworkManager` directly, we use an `APIService` protocol.

In tests, we create a `MockAPIService` that conforms to this protocol. This makes it super easy to control responses.

Here's a small snippet of how we set up a mock:

protocol APIService {
    func fetchData() async throws -> Data
}

class MockAPIService: APIService {
    var mockData: Data?
    var error: Error?

    func fetchData() async throws -> Data {
        if let error = error {
            throw error
        }
        if let data = mockData {
            return data
        }
        fatalError("Mock data not set")
    }
}

For testing navigation, we often assert that the correct `UIViewController` is presented or that a specific `URL` is opened.

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