Writing Testable Code

Workshop at The Swift Alps 2019

Transcript

1. Writing
   Testable Code
   1 — @basthomas
   

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2. Tests, what
   are they good
   for?
   2 — @basthomas
   

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3. What do you
   want to
   verify?
   3 — @basthomas
   

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4. How do you
   want to verify
   it?
   4 — @basthomas
   

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5. Dependency
   injection:
   three ways
   5 — @basthomas
   

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6. class Network {
   let urlSession: URLSession
   init(urlSession: URLSession = .shared) {
   self.urlSession = urlSession
   }
   }
   6 — @basthomas
   

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7. class Network {
   var urlSession = URLSession.shared
   }
   7 — @basthomas
   

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8. class Network {
   func request(using urlSession: URLSession = .shared) {
   }
   }
   8 — @basthomas
   

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9. Mocking
   through
   Protocols
   9 — @basthomas
   

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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
    

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11. Mocking
    through
    Subclassing
    11 — @basthomas
    

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12. class URLSessionDataTaskMock: URLSessionDataTask {
    private let closure: () -> Void
    init(closure: @escaping () -> Void) {
    self.closure = closure
    }
    override func resume() {
    closure()
    }
    }
    12 — @basthomas
    

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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
    

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14. Custom
    asserts
    14 — @basthomas
    

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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
    

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16. XCTest
    16 — @basthomas
    

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17. XCTUnwrap
    XCTNoThrow
    17 — @basthomas
    

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18. Let's talk
    about "flaky"
    18 — @basthomas
    

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19. 19 — @basthomas
    

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20. Make sure your
    architecture takes
    testability into account
    20 — @basthomas
    

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21. Tests, Code,
    Documentation
    21 — @basthomas
    

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22. Treat your
    test code like
    your real code
    22 — @basthomas
    

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23. Reviews of tests, not
    reviews with tests
    23 — @basthomas
    

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24. "Your" turn: let's take a
    look at something you
    want to have covered
    with tests
    24 — @basthomas
    

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