Implement a basic test for Fetch and fix errors it finds

tests/unit/net/fetch.rs

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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use hyper::server::{Listening, Server};
+use hyper::server::{Request as HyperRequest, Response as HyperResponse};
+use net::fetch::request::{Context, fetch, Referer, Request};
+use net_traits::response::{Response};
+use std::rc::Rc;
+use url::Url;
+
+fn make_server(message: &'static [u8]) -> (Listening, Url) {
+
+    let handler = move |_: HyperRequest, response: HyperResponse| {
+        response.send(message).unwrap();
+    };
+
+    // this is a Listening server because of handle_threads()
+    let server = Server::http("0.0.0.0:0").unwrap().handle_threads(handler, 1).unwrap();
+    let port = server.socket.port().to_string();
+    let mut url_string = "http://localhost:".to_owned();
+    url_string.push_str(&port);
+    let url = Url::parse(&url_string).unwrap();
+    (server, url)
+}
+
+
+#[test]
+fn test_fetch_response_is_not_network_error() {
+
+    static MESSAGE: &'static [u8] = b"";
+    let (mut server, url) = make_server(MESSAGE);
+
+    let mut request = Request::new(url, Context::Fetch, false);
+    request.referer = Referer::NoReferer;
+    let wrapped_request = Rc::new(request);
+
+    let fetch_response = fetch(wrapped_request, false);
+    let _ = server.close();
+
+    if Response::is_network_error(&fetch_response) {
+        panic!("fetch response shouldn't be a network error");
+    }
+}