Network Testing in Swift with DVR

Walkthrough of how to use DVR and the design behind it. Given at Realm on 2015-10-08.

Transcript

1. DVR Networking tes-ng in Swi/.
2. Hi, I'm @soffes.
3. DVR is this thing I made when I worked at Venmo.
4. Inspired by VCR for Ruby.
5. Records networking and plays it back in tests.
6. Using DVR
7. // Example XCTest func testTimeline() { let expectation = expectationWithDescription("Networking") // Your network client let client = APIClient() client.getTimeline { success in XCTAssertTrue(success) expectation.fulfill() } waitForExpectationsWithTimeout(1, handler: nil) }
8. // DVR Session let dvr = Session(cassetteName: "timeline") // Pass into initializer let client = APIClient(session: dir)
9. class APIClient { let session: NSURLSession init(session: NSURLSession = NSURLSession.sharedSession()) { self.session = session } }
10. func getTimeline(completion: Bool -> Void) { let request = NSURLRequest(URL: timelineURL) session.dataTaskWithRequest(request) { _, _, _ completion(true) }.resume() }
11. DVR Internals
12. class Session: NSURLSession { let cassetteName: String let backingSession: NSURLSession init(cassetteName: StringbackingSession: NSURLSession = NSURLSession.sharedSession()) { self.cassetteName = cassetteName self.backingSession = backingSession super.init() } override func dataTaskWithRequest(request: NSURLRequest) -> NSURLSessionDataTask { return SessionDataTask(session: self, request: request) } }
13. Call resume() & then magic.
14. class SessionDataTask: NSURLSessionDataTask { override func resume() { // Playback cassette on disk or record } }
15. Casse%es are stored as JSON.
16. { "name" : "example", "interactions" : [ { "recorded_at" : 1434688721.440751, "request" : { "method" : "GET", "url" : "http:\/\/example.com" } "response" : { "body" : "hello", "status" : 200, "url" : "http:\/\/example.com\/", "headers" : { "Cache-Control" : "max-age=604800", "Content-Type" : "text\/plain", "Last-Modified" : "Fri, 09 Aug 2013 23:54:35 GMT", "Content-Length" : "5" } } } ] }
17. Why this over mocks?
18. Mocks are inherently fragile. You have to couple your tes7ng code with the implementa7on details of your test. — Dave Abrahams, Protocol-Oriented Programming in Swi3
19. class DisabledSession: NSURLSession { override func dataTaskWithRequest(request: NSURLRequest, completionHandler: (NSData?, NSURLResponse?, NSError?) -> Void) -> NSURLSessionDataTask? { XCTFail("Networking disabled") return nil } }
20. github.com/venmo/DVR
21. Thanks