URLProtocolMock.swift

//
//  URLProtocolMock.swift
//  WeatherKitTests
//
//  Created by Kraig Spear on 12/15/19.
//  Copyright © 2019 spearware. All rights reserved.
//

import Foundation
import XCTest

class URLProtocolMock: URLProtocol {
    static var testUrls: [URL: Data] = [:]
    
    override class func canInit(with request: URLRequest) -> Bool {
        true
    }
    
    override class func canInit(with task: URLSessionTask) -> Bool {
        true
    }
    
    override class func canonicalRequest(for request: URLRequest) -> URLRequest {
        request
    }
    
    override func startLoading() {
        guard let client = self.client else {
            XCTFail("missing client")
            return
        }
        
        guard let url = self.request.url else {
            XCTFail("Request URL missing")
            return
        }
        
        guard let data = URLProtocolMock.testUrls[url] else {
            XCTFail("No data for URL")
            return
        }
        
        let response = HTTPURLResponse(url: url,
                                       statusCode: 200,
                                       httpVersion: nil,
                                       headerFields: nil)!
        
        client.urlProtocol(self, didReceive: response, cacheStoragePolicy: .notAllowed)
        client.urlProtocol(self, didLoad: data)
        
        client.urlProtocolDidFinishLoading(self)
    }
    
    override func stopLoading() {}
}

// Usage

 func testRadarTimesLoadedFromNetworkWhenCacheDoesNotExist() {
        
        let url = URL(string: "https://tilecache.rainviewer.com/api/maps.json")!
        let data = TestDataLoader.loadData(forResource: "RadarTimes")
        URLProtocolMock.testUrls = [url: data]
        
        let expect = expectation(description: "radarTimeLoaded")
        
        radarTimeLoadedCancel = radarTimeLoader.radarTimes.sink(receiveCompletion: { completed in
            
            switch completed {
            case .failure:
                XCTFail("Unexpected failure")
            case .finished:
                expect.fulfill()
            }
            
        }) { times in
            XCTAssertEqual(13, times.count)
        }
        
        XCTAssertEqual(.completed, XCTWaiter().wait(for: [expect], timeout: 1))
    }