Fetch tests (first batch) (#3977)

* Customizable fetch

* Some basic Fetch tests

dapps/src/tests/helpers/fetch.rs

@@ -0,0 +1,64 @@
+// Copyright 2015, 2016 Parity Technologies (UK) Ltd.
+// This file is part of Parity.
+
+// Parity is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
+
+use std::{io, thread};
+use std::sync::Arc;
+use std::sync::atomic::{self, AtomicUsize};
+use util::Mutex;
+
+use futures::{self, Future};
+use fetch::{self, Fetch};
+
+#[derive(Clone, Default)]
+pub struct FakeFetch {
+	asserted: Arc<AtomicUsize>,
+	requested: Arc<Mutex<Vec<String>>>,
+}
+
+impl FakeFetch {
+	pub fn assert_requested(&self, url: &str) {
+		let requests = self.requested.lock();
+		let idx = self.asserted.fetch_add(1, atomic::Ordering::SeqCst);
+
+		assert_eq!(requests.get(idx), Some(&url.to_owned()), "Expected fetch from specific URL.");
+	}
+
+	pub fn assert_no_more_requests(&self) {
+		let requests = self.requested.lock();
+		let len = self.asserted.load(atomic::Ordering::SeqCst);
+		assert_eq!(requests.len(), len, "Didn't expect any more requests, got: {:?}", &requests[len..]);
+	}
+}
+
+impl Fetch for FakeFetch {
+	type Result = futures::BoxFuture<fetch::Response, fetch::Error>;
+
+	fn new() -> Result<Self, fetch::Error> where Self: Sized {
+		Ok(FakeFetch::default())
+	}
+
+	fn fetch_with_abort(&self, url: &str, _abort: fetch::Abort) -> Self::Result {
+		self.requested.lock().push(url.into());
+
+		let (tx, rx) = futures::oneshot();
+		thread::spawn(move || {
+			let cursor = io::Cursor::new(b"Some content");
+			tx.complete(fetch::Response::from_reader(cursor));
+		});
+
+		rx.map_err(|_| fetch::Error::Aborted).boxed()
+	}
+}