Example of dataTask producing a double callback on Swift 5 in linux

dataTask.swift

import XCTest
import Kitura
import Foundation

final class dataTaskTests: XCTestCase {
	let router = Router()
	
    func testExample() throws {
		router.get("/", handler: getHandler)
		Kitura.addHTTPServer(onPort: 8080, with: router)
		Kitura.start()
		
		let expectation1 = expectation(description: "A unauthorized response is received from the server -> .unauthorized")

		let request = URLRequest(url: URL(string: "http://localhost:8080/")!)
		let session = URLSession(configuration: URLSessionConfiguration.default)
		let task = session.dataTask(with: request) { (data, response, error) in
			print("session.dataTask: \(String(describing: response?.description))")
			guard error == nil, let response = response as? HTTPURLResponse else {
				print("Error returned: \(String(describing: error?.localizedDescription))")
				return XCTFail("Error connecting returned")
			}
			
			let code = response.statusCode
			if code >= 200 && code < 300 {
				print("Success code")
				return XCTFail()
			} else {
				print("Failure code")
				expectation1.fulfill()
			}
		}
		task.resume()
		waitForExpectations(timeout: 3.0, handler: nil)
		Kitura.stop()
    }

	func getHandler(completion: ([String]?, RequestError?) -> Void) {
		completion(nil, .unauthorized)
	}

    static var allTests = [
        ("testExample", testExample),
    ]
}