implementation of redirected property (#197)

* implementation of redirected property

* improved inline docs

docs/api.md

@@ -43,6 +43,7 @@ Replaces `fetch()` with a stub which records its calls, grouped by route, and op
     * `headers`: key/value map of headers to match
     * `matcher`: as specified above
     * `response`: as specified above
+    * `__redirectUrl`: *experimental* the url the response should be from (to imitate followed redirects - will set `redirected: true` on the response)
     * `times`: An integer, `n`, limiting the number of times the matcher can be used. If the route has already been called `n` times the route will be ignored and the call to `fetch()` will fall through to be handled by any other routes defined (which may eventually result in an error if nothing matches it)
 
 #### `once()`

src/fetch-mock.js

@@ -144,43 +144,70 @@ FetchMock.prototype.mockResponse = function (url, responseConfig, fetchOpts, res
 		responseConfig = responseConfig(url, fetchOpts);
 	}
 
+	// If the response is a pre-made Response, respond with it
 	if (FetchMock.Response.prototype.isPrototypeOf(responseConfig)) {
 		return this.respond(Promise.resolve(responseConfig), resolveHoldingPromise);
 	}
 
+	// If the response says to throw an error, throw it
 	if (responseConfig.throws) {
 		return this.respond(Promise.reject(responseConfig.throws), resolveHoldingPromise);
 	}
 
+	// If the response config looks like a status, start to generate a simple response
 	if (typeof responseConfig === 'number') {
 		responseConfig = {
 			status: responseConfig
 		};
-	} else if (typeof responseConfig === 'string' || !(responseConfig.body || responseConfig.headers || responseConfig.throws || responseConfig.status)) {
+	// If the response config is not an object, or is an object that doesn't use
+	// any reserved properties, assume it is meant to be the body of the response
+	} else if (typeof responseConfig === 'string' || !(
+		responseConfig.body ||
+		responseConfig.headers ||
+		responseConfig.throws ||
+		responseConfig.status ||
+		responseConfig.__redirectUrl
+	)) {
 		responseConfig = {
 			body: responseConfig
 		};
 	}
 
+	// Now we are sure we're dealing with a response config object, so start to
+	// construct a real response from it
 	const opts = responseConfig.opts || {};
-	opts.url = url;
-	opts.sendAsJson = responseConfig.sendAsJson === undefined ? FetchMock.config.sendAsJson : responseConfig.sendAsJson;
+
+	// set the response url
+	opts.url = responseConfig.__redirectUrl || url;
+
+	// Handle a reasonably common misuse of the library - returning an object
+	// with the property 'status'
 	if (responseConfig.status && (typeof responseConfig.status !== 'number' || parseInt(responseConfig.status, 10) !== responseConfig.status || responseConfig.status < 200 || responseConfig.status > 599)) {
 		throw new TypeError(`Invalid status ${responseConfig.status} passed on response object.
 To respond with a JSON object that has status as a property assign the object to body
 e.g. {"body": {"status: "registered"}}`);
 	}
+
+	// set up the response status
 	opts.status = responseConfig.status || 200;
 	opts.statusText = FetchMock.statusTextMap['' + opts.status];
-	// The ternary operator is to cope with new Headers(undefined) throwing in Chrome
+
+	// Set up response headers. The ternary operator is to cope with
+	// new Headers(undefined) throwing in Chrome
 	// https://code.google.com/p/chromium/issues/detail?id=335871
 	opts.headers = responseConfig.headers ? new FetchMock.Headers(responseConfig.headers) : new FetchMock.Headers();
 
+	// start to construct the body
 	let body = responseConfig.body;
+
+	// convert to json if we need to
+	opts.sendAsJson = responseConfig.sendAsJson === undefined ? FetchMock.config.sendAsJson : responseConfig.sendAsJson;
 	if (opts.sendAsJson && responseConfig.body != null && typeof body === 'object') { //eslint-disable-line
 		body = JSON.stringify(body);
 	}
 
+	// On the server we need to manually construct the readable stream for the
+	// Response object (on the client this is done automatically)
 	if (FetchMock.stream) {
 		let s = new FetchMock.stream.Readable();
 		if (body != null) { //eslint-disable-line
@@ -189,8 +216,19 @@ e.g. {"body": {"status: "registered"}}`);
 		s.push(null);
 		body = s;
 	}
+	let response = new FetchMock.Response(body, opts);
+
+	// When mocking a followed redirect we must wrap the response in an object
+	// which sets the redirected flag (not a writable property on the actual response)
+	if (responseConfig.__redirectUrl) {
+		response = Object.create(response, {
+			redirected: {
+				value: true
+			}
+		})
+	}
 
-	return this.respond(Promise.resolve(new FetchMock.Response(body, opts)), resolveHoldingPromise);
+	return this.respond(Promise.resolve(response), resolveHoldingPromise);
 }
 
 FetchMock.prototype.respond = function (response, resolveHoldingPromise) {
@@ -351,4 +389,5 @@ FetchMock.prototype.sandbox = function (Promise) {
 		}
 	})
 
+
 module.exports = FetchMock;

test/spec.js

@@ -819,6 +819,22 @@ module.exports = (fetchMock, theGlobal, Request, Response) => {
 						});
 				});
 
+				it('respond with a redirected response', () => {
+					fetchMock.mock('http://it.at.there/', {
+						__redirectUrl: 'http://it.at.there/destination',
+						body: 'I am a redirect'
+					});
+					return fetch('http://it.at.there/')
+						.then(res => {
+							expect(res.redirected).to.equal(true);
+							expect(res.url).to.equal('http://it.at.there/destination');
+							return res.text()
+								.then(text => {
+									expect(text).to.equal('I am a redirect')
+								})
+						});
+				});
+
 				it('construct a response based on the request', () => {
 					fetchMock.mock({
 						name: 'route',