swift - 如何模拟DataTaskPublisher？

Question

我正在尝试使用 URLSession.DataTaskPublisher 为我的 API 编写一些单元测试。我在 Stackoverflow 上发现了一个已经存在的问题，但我正在努力使用建议的解决方案来实现一个工作类。

这是现有的问题:How to mock URLSession.DataTaskPublisher

protocol APIDataTaskPublisher {
    func dataTaskPublisher(for request: URLRequest) -> URLSession.DataTaskPublisher
}

class APISessionDataTaskPublisher: APIDataTaskPublisher {
    func dataTaskPublisher(for request: URLRequest) -> URLSession.DataTaskPublisher {
        return session.dataTaskPublisher(for: request)
    }

    var session: URLSession

    init(session: URLSession = URLSession.shared) {
        self.session = session
    }
}

class URLSessionMock: APIDataTaskPublisher {
    func dataTaskPublisher(for request: URLRequest) -> URLSession.DataTaskPublisher {
        // How can I return a mocked URLSession.DataTaskPublisher here?
    }
}

我的 API 然后像这样使用上面的内容:

class MyAPI {
    /// Shared URL session
    private let urlSession: APIDataTaskPublisher

    init(urlSession: APIDataTaskPublisher = APISessionDataTaskPublisher(session: URLSession.shared)) {
        self.urlSession = urlSession
    }
}

我不知道如何实现 URLSessionMock.dataTaskPublisher()。

Answer 1

模拟 DataTaskPublisher 可能会更简单不。您真的关心发布者是否是 DataTaskPublisher 吗？可能不会。您可能关心的是获得与 DataTaskPublisher 相同的 Output 和 Failure 类型。因此，更改您的 API 以仅指定:

protocol APIProvider {
    typealias APIResponse = URLSession.DataTaskPublisher.Output
    func apiResponse(for request: URLRequest) -> AnyPublisher<APIResponse, URLError>
}

使 URLSession 符合生产用途:

extension URLSession: APIProvider {
    func apiResponse(for request: URLRequest) -> AnyPublisher<APIResponse, URLError> {
        return dataTaskPublisher(for: request).eraseToAnyPublisher()
    }
}

然后您的模拟可以以任何方便的方式创建发布者。例如:

struct MockAPIProvider: APIProvider {
    func apiResponse(for request: URLRequest) -> AnyPublisher<APIResponse, URLError> {
        let response = HTTPURLResponse(url: request.url!, statusCode: 200, httpVersion: "HTTP/1.1", headerFields: nil)!
        let data = "Hello, world!".data(using: .utf8)!
        return Just((data: data, response: response))
            .setFailureType(to: URLError.self)
            .eraseToAnyPublisher()
    }
}