mixing in the ability to send an explicit error from a mock response (#…

…52)

* mixing in the ability to send an explicit error from a mock response in order to test error handling

* adding a test to verify the code works and show how it might be used

* adding a note to README for how to request an error response from a mock

MockerTests/MockerTests.swift

@@ -346,4 +346,34 @@ final class MockerTests: XCTestCase {
         request.httpMethod = Mock.HTTPMethod.put.rawValue
         XCTAssertNotNil(Mocker.mock(for: request))
     }
+
+    /// it should return the error we requested from the mock when we pass in an Error.
+    func testMockReturningError() {
+        let expectation = self.expectation(description: "Data request should succeed")
+        let originalURL = URL(string: "https://www.wetransfer.com/example.json")!
+
+        enum TestExampleError: Error {
+            case example
+        }
+
+        Mock(url: originalURL, dataType: .json, statusCode: 500, data: [.get: Data()], requestError: TestExampleError.example).register()
+
+        URLSession.shared.dataTask(with: originalURL) { (data, urlresponse, err) in
+
+            XCTAssertNil(data)
+            XCTAssertNil(urlresponse)
+            XCTAssertNotNil(err)
+            if let err = err {
+                // there's not a particularly elegant way to verify an instance
+                // of an error, but this is a convenient workaround for testing
+                // purposes
+                XCTAssertEqual("example", String(describing: err))
+            }
+
+            expectation.fulfill()
+        }.resume()
+
+        waitForExpectations(timeout: 10.0, handler: nil)
+
+    }
 }

README.md

@@ -203,6 +203,28 @@ mock.completion = {
 mock.register()
 ```
 
+##### Mock errors
+
+You can request a `Mock` to return an error, allowing testing of error handling.
+
+```swift
+Mock(url: originalURL, dataType: .json, statusCode: 500, data: [.get: Data()],
+     requestError: TestExampleError.example).register()
+
+URLSession.shared.dataTask(with: originalURL) { (data, urlresponse, err) in
+    XCTAssertNil(data)
+    XCTAssertNil(urlresponse)
+    XCTAssertNotNil(err)
+    if let err = err {
+        // there's not a particularly elegant way to verify an instance
+        // of an error, but this is a convenient workaround for testing
+        // purposes
+        XCTAssertEqual("example", String(describing: err))
+    }
+
+    expectation.fulfill()
+}.resume()
+```
 
 ## Communication
 

Sources/Mock.swift

@@ -60,6 +60,9 @@ public struct Mock: Equatable {
     /// The type of the data which is returned.
     public let dataType: DataType
 
+    /// If set, the error that URLProtocol will report as a result rather than returning data from the mock
+    public let requestError: Error?
+
     /// The headers to send back with the response.
     public let headers: [String: String]
 
@@ -101,14 +104,15 @@ public struct Mock: Equatable {
     /// The callback which will be executed everytime this `Mock` was started. Can be used within unit tests for validating that a request has been started. The callback must be set before calling `register`.
     public var onRequest: OnRequest?
 
-    private init(url: URL? = nil, ignoreQuery: Bool = false, dataType: DataType, statusCode: Int, data: [HTTPMethod: Data], additionalHeaders: [String: String] = [:], fileExtensions: [String]? = nil) {
+    private init(url: URL? = nil, ignoreQuery: Bool = false, dataType: DataType, statusCode: Int, data: [HTTPMethod: Data], requestError: Error? = nil, additionalHeaders: [String: String] = [:], fileExtensions: [String]? = nil) {
         self.urlToMock = url
         let generatedURL = URL(string: "https://mocked.wetransfer.com/\(dataType.rawValue)/\(statusCode)/\(data.keys.first!.rawValue)")!
         self.generatedURL = generatedURL
         var request = URLRequest(url: url ?? generatedURL)
         request.httpMethod = data.keys.first!.rawValue
         self.request = request
         self.ignoreQuery = ignoreQuery
+        self.requestError = requestError
         self.dataType = dataType
         self.statusCode = statusCode
         self.data = data
@@ -136,12 +140,13 @@ public struct Mock: Equatable {
     /// - Parameters:
     ///   - url: The URL to match for and to return the mocked data for.
     ///   - ignoreQuery: If `true`, checking the URL will ignore the query and match only for the scheme, host and path. Defaults to `false`.
+    ///   - reportFailure: if `true`, the URLsession will report an error loading the URL rather than returning data. Defaults to `false`.
     ///   - dataType: The type of the data which is returned.
     ///   - statusCode: The HTTP status code to return with the response.
     ///   - data: The data which will be returned as the response based on the HTTP Method.
     ///   - additionalHeaders: Additional headers to be added to the response.
-    public init(url: URL, ignoreQuery: Bool = false, dataType: DataType, statusCode: Int, data: [HTTPMethod: Data], additionalHeaders: [String: String] = [:]) {
-        self.init(url: url, ignoreQuery: ignoreQuery, dataType: dataType, statusCode: statusCode, data: data, additionalHeaders: additionalHeaders, fileExtensions: nil)
+    public init(url: URL, ignoreQuery: Bool = false, dataType: DataType, statusCode: Int, data: [HTTPMethod: Data], additionalHeaders: [String: String] = [:], requestError: Error? = nil) {
+        self.init(url: url, ignoreQuery: ignoreQuery, dataType: dataType, statusCode: statusCode, data: data, requestError: requestError, additionalHeaders: additionalHeaders, fileExtensions: nil)
     }
 
     /// Creates a `Mock` for the given file extensions. The mock will only be used for urls matching the extension.

Sources/MockingURLProtocol.swift

@@ -13,6 +13,7 @@ public final class MockingURLProtocol: URLProtocol {
 
     enum Error: Swift.Error, LocalizedError, CustomDebugStringConvertible {
         case missingMockedData(url: String)
+        case explicitMockFailure(url: String)
 
         var errorDescription: String? {
             return debugDescription
@@ -22,6 +23,8 @@ public final class MockingURLProtocol: URLProtocol {
             switch self {
             case .missingMockedData(let url):
                 return "Missing mock for URL: \(url)"
+            case .explicitMockFailure(url: let url):
+                return "Induced error for URL: \(url)"
             }
         }
     }
@@ -60,6 +63,8 @@ public final class MockingURLProtocol: URLProtocol {
     private func finishRequest(for mock: Mock, data: Data, response: HTTPURLResponse) {
         if let redirectLocation = data.redirectLocation {
             self.client?.urlProtocol(self, wasRedirectedTo: URLRequest(url: redirectLocation), redirectResponse: response)
+        } else if let requestError = mock.requestError {
+            self.client?.urlProtocol(self, didFailWithError: requestError)
         } else {
             self.client?.urlProtocol(self, didReceive: response, cacheStoragePolicy: .notAllowed)
             self.client?.urlProtocol(self, didLoad: data)