Unit testing network calls (failing tests) - Swift - ios

Question

I'm trying to write failing tests for my network calls but can't find anyway to access the connection settings from within my tests.
This code works fine for testing a success case:
func testRetrieveProducts() {
let expectation = expectationWithDescription("asynchronous request")
Requests().retrieveProducts({ (products) -> () in
// check that we have two arrays returned.
XCTAssert(products.count == 2)
expectation.fulfill()
}) { (error) -> () in
XCTFail("Request failed")
}
waitForExpectationsWithTimeout(5.0, handler: nil)
}
But I've been looking for a way to test network timeouts, and incorrect data being returned.
I can probably test incorrect data by calling functions individually inside the retrieveProducts function and stubbing stuff out, but doing something as simple as turning off the internet is proving to be quite difficult.
I know we have access to the Network Link Conditioner, but turning this on and off for each test isn't an option.
I'd love to have access to something as simple as:
func testFailRetrieveProducts() {
let expectation = expectationWithDescription("asynchronous request")
SomeNetworkClass.disableInternet()
Requests().retrieveProducts({ (products) -> () in
}) { (error) -> () in
XCTAssert(error == SomeError.TimeoutError)
}
waitForExpectationsWithTimeout(5.0, handler: nil)
}
Any solutions out there that can handle what I'm after, or am I going about this all wrong?

Answer 1

Take a look at this NSHipster article about Apple's Network Link Conditioner. There's a lot of presets and you can create your own custom network profile. Unfortunately there doesn't seem to be a way to throttle the network in code.
A somewhat viable alternative however is to use ReactiveCocoa and model all your network events as SignalProducers. Then you can use the throttle or wait function, depending on your intentions.

Answer 2

I ended up just mocking the network calls, which to be honest is a lot better than performing tests over an actual connection, as these can be very unreliable anyway.
Here's my mock NSURLSession
class MockSession: NSURLSession {
var completionHandler:((NSData!, NSURLResponse!, NSError!) -> Void)?
static var mockResponse: (data: NSData?, urlResponse: NSURLResponse?, error: NSError?)
override class func sharedSession() -> NSURLSession {
return MockSession()
}
override func dataTaskWithRequest(request: NSURLRequest, completionHandler: (NSData?, NSURLResponse?, NSError?) -> Void) -> NSURLSessionDataTask {
self.completionHandler = completionHandler
return MockTask(response: MockSession.mockResponse, completionHandler: completionHandler)
}
class MockTask: NSURLSessionDataTask {
typealias Response = (data: NSData?, urlResponse: NSURLResponse?, error: NSError?)
var mockResponse: Response
let completionHandler: ((NSData!, NSURLResponse!, NSError!) -> Void)?
init(response: Response, completionHandler:((NSData!, NSURLResponse!, NSError!) -> Void)?) {
self.mockResponse = response
self.completionHandler = completionHandler
}
override func resume() {
completionHandler!(mockResponse.data, mockResponse.urlResponse, mockResponse.error)
}
}
}
Here's how I use it in a test:
Note that you still have to use an expectation even though there's no network delay.
func testRetrieveProductsValidResponse() {
let testBundle = NSBundle(forClass: self.dynamicType)
let filepath = testBundle.pathForResource("products", ofType: "txt")
let data = NSData(contentsOfFile: filepath!)
let urlResponse = NSHTTPURLResponse(URL: NSURL(string: "https://anyURL.com")!, statusCode: 200, HTTPVersion: nil, headerFields: nil)
MockSession.mockResponse = (data, urlResponse: urlResponse, error: nil)
let requestsClass = RequestManager()
requestsClass.Session = MockSession.self
let expectation = expectationWithDescription("ready")
requestsClass.retrieveProducts("N/R FOR TEST", branchID: "N/R FOR TEST", products: { (products) -> () in
XCTAssertTrue(products.count == 7)
expectation.fulfill()
}) { (error) -> () in
XCTAssertFalse(error == Errors.NetworkError, "Its a network error")
XCTAssertFalse(error == Errors.ParseError, "Its a parse error")
XCTFail("Error not covered by previous asserts. Shouln't get to here anyway.")
expectation.fulfill()
}
waitForExpectationsWithTimeout(3.0, handler: nil)
}
Finally, I have an accessible property on my RequestManager class that I can swap out with the MockSession when doing my tests.
var Session = NSURLSession.self