无法将类型'（Data？）->（）'的值转换为预期的参数类型'（_）->（）'

Question

I created a function to retrieve json data from a network server. It works properly when run in a production environment but when it's setup to be unit-tested the error : Cannot convert value of type '(Data?) -> ()' to expected argument type '(_) -> ()' . Here is the function:

func getJSONData <T : Codable> (url: ServerUrl, type: T.Type, completionHandler:@escaping (_ details: T) -> ())  {

    guard let url = URL(string: baseURL + url.rawValue) else { return }


    session.dataTask(with: url, completionHandler: {
        (data, response, err) in

        guard err == nil else {
        print("There was a network error:", err as Any)
        return
        }
        guard let data = data else { return }

        do {

            let updatedModels = try JSONDecoder().decode(T.self, from: data)
            completionHandler(updatedModels)

        } catch let jsonErr {
            print("Error serializing json:", jsonErr)
            return }

        }).resume()
}

Here it is in the unit test:

func test_getJSONData_should_return_data() {

var actualData: Data?

sut.getJSONData(url: ServerUrl.colors, type: MainColor.self, completionHandler: { (data) in //error here

    actualData = data

})
XCTAssertNotNil(actualData)

}

Answer 1

问题是MainColor返回类型MainColor值不是Data ，这应该是

var actualData: MainColor?