Writing Testable Code

Workshop at The Swift Alps 2019

Transcript

1. Writing Testable Code 1 — @basthomas
2. Tests, what are they good for? 2 — @basthomas
3. What do you want to verify? 3 — @basthomas
4. How do you want to verify it? 4 — @basthomas
5. Dependency injection: three ways 5 — @basthomas
6. class Network { let urlSession: URLSession init(urlSession: URLSession = .shared) { self.urlSession = urlSession } } 6 — @basthomas
7. class Network { var urlSession = URLSession.shared } 7 — @basthomas
8. class Network { func request(using urlSession: URLSession = .shared) { } } 8 — @basthomas
9. Mocking through Protocols 9 — @basthomas
10. protocol UIApplicationProtocol { func canOpenURL(_ url: URL) -> Bool func open( _ url: URL, options: [UIApplication.OpenExternalURLOptionsKey : Any], completionHandler completion: ((Bool) -> Void)? ) } extension UIApplication: UIApplicationProtocol {} 10 — @basthomas
11. Mocking through Subclassing 11 — @basthomas
12. class URLSessionDataTaskMock: URLSessionDataTask { private let closure: () -> Void init(closure: @escaping () -> Void) { self.closure = closure } override func resume() { closure() } } 12 — @basthomas
13. class URLSessionMock: URLSession { var data: Data? var error: Error? override func dataTask( with url: URL, completionHandler: @escaping (Data?, URLResponse?, Error?) -> Void ) -> URLSessionDataTask { let data = self.data let error = self.error return URLSessionDataTaskMock { completionHandler(data, nil, error) } } } 13 — @basthomas
14. Custom asserts 14 — @basthomas
15. func assertManyThings( cookie: Cookie, file: StaticString = #file, line: UInt = #line ) { XCTAssertTrue(cookie.isDoughy, file: file, line: line) XCTAssertLessThan(cookie.calories, 200, file: file, line: line) } 15 — @basthomas
16. XCTest 16 — @basthomas
17. XCTUnwrap XCTNoThrow 17 — @basthomas
18. Let's talk about "flaky" 18 — @basthomas
19. 19 — @basthomas
20. Make sure your architecture takes testability into account 20 — @basthomas
21. Tests, Code, Documentation 21 — @basthomas
22. Treat your test code like your real code 22 — @basthomas
23. Reviews of tests, not reviews with tests 23 — @basthomas
24. "Your" turn: let's take a look at something you want to have covered with tests 24 — @basthomas