Unit test - result0924/iosLearning GitHub Wiki

A PATTERN FOR WRITING GOOD TESTS

• Arrange: 初始化的過程(Giver a client and a sut)
• Act: 執行測試的目標，並取得實際結果(When we invoke sut.load())
• Assert: 驗證結果(Then assert that a URL request was initiated in the client)

How to mock singleton

• Refer: Move test logic to a separate type HTTPClientSpy

1. Make the shared instance a variable

static let shared = HTTPClient() -> static var shared = HTTPClient()

2. Move the test logic from RemoteFeedLoader to HTTPClient

HTTPClient.shared.requestedURL = URL(string: "https://a-url.com") -> 
HTTPClient.shared.get(from: URL(string: "https://a-url.com"))

3. Move the test logic to a new subclass of HTTPClient.(the spy that it is targeting, the test specifically)

class HTTPClientSpy: HTTPClient {
    ....
}

4. Swap the HTTPClient shared instance with the spy subclass during tests.
5. Remove HTTPClient private initializer since it's not a Singleton anymore.

Note

• Spy is just an implementation of the protocol rather than a subtype of the abstract class

Refer

• Hello Testing