Replacing URL with URLRequest

URLRequestForURL.swift

import PlaygroundSupport

let url = URL(string: "https://picsum.photos/200/300")!

private extension URLSession {
    /// Method under test
    func urlRequest(with url: URL) -> URLRequest {
        return URLRequest(
            url: url,
            cachePolicy: configuration.requestCachePolicy,
            timeoutInterval: configuration.timeoutIntervalForRequest
        )
    }
}

func testAgainst(configuration: URLSessionConfiguration) {
    let session = URLSession(configuration: configuration)

    var taskFromURLRef: URLSessionTask?
    var taskFromRequestRef: URLSessionTask?

    let taskFromURL = session.dataTask(with: url) { data, response, error in
        print("Inspecting request for `.dataTask(with: url)`")
        inspectCurrentRequestFor(task: taskFromURLRef!)
    }

    let request = session.urlRequest(with: url)
    let taskFromRequest = session.dataTask(with: request) { data, response, error in
        print("Inspecting request for `.dataTask(with: request)`")
        inspectCurrentRequestFor(task: taskFromRequestRef!)
    }

    taskFromURLRef = taskFromURL
    taskFromRequestRef = taskFromRequest

    taskFromURL.resume()
    taskFromRequest.resume()

    sleep(4) // wait for requests completion
}

func inspectCurrentRequestFor(task: URLSessionTask) {
    print(" → allHTTPHeaderFields:", task.currentRequest!.allHTTPHeaderFields!.sorted(by: <).map { k, v in "\(k): \(v)" })
    print(" → networkServiceType:", task.currentRequest!.networkServiceType.rawValue)
    print(" → allowsCellularAccess:", task.currentRequest!.allowsCellularAccess)
    print(" → timeoutInterval", task.currentRequest!.timeoutInterval)
    print(" → httpShouldHandleCookies", task.currentRequest!.httpShouldHandleCookies)
}

testAgainst(configuration: {
    let configuration = URLSessionConfiguration.ephemeral
    configuration.httpAdditionalHeaders = ["foo": "bar"]
    configuration.networkServiceType = .avStreaming
    configuration.allowsCellularAccess = false
    configuration.timeoutIntervalForRequest = 13
    configuration.timeoutIntervalForResource = 11
    configuration.httpCookieAcceptPolicy = .always
    configuration.httpShouldSetCookies = true
    return configuration
}())

PlaygroundPage.current.needsIndefiniteExecution = true

Output:

Inspecting request for `.dataTask(with: url)`
 → allHTTPHeaderFields: ["Accept: */*", "Accept-Encoding: gzip, deflate, br", "Accept-Language: en-us", "foo: bar"]
 → networkServiceType: 0
 → allowsCellularAccess: true
 → timeoutInterval 60.0
 → httpShouldHandleCookies true
Inspecting request for `.dataTask(with: request)`
 → allHTTPHeaderFields: ["Accept: */*", "Accept-Encoding: gzip, deflate, br", "Accept-Language: en-us", "foo: bar"]
 → networkServiceType: 0
 → allowsCellularAccess: true
 → timeoutInterval 13.0 ⚠️
 → httpShouldHandleCookies true