Write unit test for function that uses URLSession and RxSwift - swift

Question

I have a function that creates and returns Observable that downloads and decodes data using URLSession. I wanted to write unit test for this function but have no idea how to tackle it.
function:
func getRecipes(query: String, _ needsMoreData: Bool) -> Observable<[Recipes]> {
guard let url = URL(string: "https://api.spoonacular.com/recipes/search?\(query)&apiKey=myApiKey") else {
return Observable.just([])
}
return Observable.create { observer in
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data else {
return
}
do {
if self.recipes == nil {
self.recipes = try self.decoder.decode(Recipes.self, from: data)
self.dataList = self.recipes.results
self.baseUrl = self.recipes.baseUrl
} else {
if needsMoreData {
self.recipes = try self.decoder.decode(Recipes.self, from: data)
self.dataList.append(contentsOf: self.recipes.results.suffix(50))
} else {
self.dataList = try self.decoder.decode(Recipes.self, from: data).results
}
}
observer.onCompleted()
} catch let error {
observer.onError(error)
}
}
task.resume()
return Disposables.create {
task.cancel()
}
}
.trackActivity(activityIndicator)
}

Answer 1

The obvious answer is to inject the dataTask instead of using the singleton inside your function. Something like this:
func getRecipes(query: String, _ needsMoreData: Bool, dataTask: #escaping (URL, #escaping (Data?, URLResponse?, Error?) -> Void) -> URLSessionDataTask) -> Observable<[Recipes]> {
guard let url = URL(string: "https://api.spoonacular.com/recipes/search?\(query)&apiKey=myApiKey") else {
return Observable.just([])
}
return Observable.create { observer in
let task = dataTask(url) { (data, response, error) in
// and so on...
You would call it in the main code like this:
getRecipes(query: "", false, dataTask: URLSession.shared.dataTask(with:completionHandler:))
In your test, you would need something like this:
func fakeDataTask(_ url: URL, _ completionHandler: #escaping (Data?, URLResponse?, Error?) -> Void) -> URLSessionDataTask {
XCTAssertEqual(url, expectedURL)
completionHandler(testData, nil, nil)
return URLSessionDataTask()
}
let result = getRecipes(query: "", false, dataTask: fakeDataTask)
Did you know that URLSession has Reactive extensions already created for it? The one I like best is: URLSession.shared.rx.data(request:) which returns an Observable which will emit an error if there are any problems getting the data. I suggest you use it.