Xcode UI Testing - How to mock network data

UI Testing - Mocking Network Data

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_README.md

UI Testing - Mocking Network Data

1. Create a Configuration object that provides an instance of NSURLSession. When running under UI Testing return a seeded one, otherwise use the default one.
2. Grab a NSURLSession from the configuration in your HTTP client.
3. Subclass NSURLSession to use seeded data when appropriate.
4. Seed your response JSON in your UI Tests.

Configuration.swift

import Foundation

struct Config {
    static let urlSession: NSURLSession = UITesting() ? SeededURLSession() : NSURLSession.defaultSession()
}

private func UITesting() -> Bool {
    return NSProcessInfo.processInfo().arguments.contains("UI-TESTING")
}

HTTPClient.swift

import Foundation

typealias HTTPResult = (NSData?, ErrorType?) -> Void

class HTTPClient {
    private let session: NSURLSession

    init(session: NSURLSession = Config.urlSession) {
        self.session = session
    }

    func get(url: NSURL, completion: HTTPResult) {
        let task = session.dataTaskWithURL(url) { (data, response, error) -> Void in
            // ... //
        }
        task.resume()
    }
}

NSURLSession+MainQueue.swift

import Foundation

extension NSURLSession {
    static func defaultSession() -> NSURLSession {
        return NSURLSession(configuration: NSURLSessionConfiguration.defaultSessionConfiguration(),
            delegate: nil, delegateQueue: NSOperationQueue.mainQueue())
    }
}

SeededURLSession.swift

import Foundation

typealias DataCompletion = (NSData?, NSURLResponse?, NSError?) -> Void

class SeededURLSession: NSURLSession {
    override func dataTaskWithURL(url: NSURL, completionHandler: DataCompletion) -> NSURLSessionDataTask {
        return SeededDataTask(url: url, completion: completionHandler)
    }
}

class SeededDataTask: NSURLSessionDataTask {
    private let url: NSURL
    private let completion: DataCompletion
    private let realSession = NSURLSession.defaultSession()

    init(url: NSURL, completion: DataCompletion) {
        self.url = url
        self.completion = completion
    }

    override func resume() {
        guard let json = NSProcessInfo.processInfo().environment[url.absoluteString]
            else { realSession.dataTaskWithURL(url, completionHandler: completion); return }

        let response = NSHTTPURLResponse(URL: url, statusCode: 200, HTTPVersion: nil, headerFields: nil)
        let data = json.dataUsingEncoding(NSUTF8StringEncoding)
        completion(data, response, nil)
    }
}

UITests.swift

import XCTest

class UITests: XCTestCase {
    let app = XCUIApplication()
    let postCount = "33"

    override func setUp() {
        super.setUp()
        continueAfterFailure = false

        app.launchArguments += ["UI-TESTING"]
        app.launchEnvironment["http://masilotti.com/api/posts.json"] = "{\"posts\": \(postCount)}"
        app.launch()
    }

    func test_DisplaysPostCount() {
        let postCountLabel = app.staticTexts[postCount]
        waitForElementToAppear(postCountLabel)
    }

    private func waitForElementToAppear(element: XCUIElement, file: String = __FILE__, line: UInt = __LINE__) {
        let existsPredicate = NSPredicate(format: "exists == true")
        expectationForPredicate(existsPredicate, evaluatedWithObject: element, handler: nil)

        waitForExpectationsWithTimeout(5) { (error) -> Void in
            if (error != nil) {
                let message = "Failed to find \(element) after 5 seconds."
                self.recordFailureWithDescription(message, inFile: file, atLine: line, expected: true)
            }
        }
    }
}