diff --git a/substrate/candidate-agreement/src/bft.rs b/substrate/candidate-agreement/src/bft.rs
index 03c67fcb0f..f41bfd4606 100644
--- a/substrate/candidate-agreement/src/bft.rs
+++ b/substrate/candidate-agreement/src/bft.rs
@@ -58,12 +58,13 @@ pub struct LocalizedMessage<P, V> {
 // TODO: consider cross-view committing?
 // TODO: impl future.
 pub fn agree<'a, P, I, O, V>(local_proposal: P, input: I, output: O, max_faulty: usize)
-	-> Box<Future<Item=P, Error=I::Error> + 'a>
+	-> Box<Future<Item=P, Error=I::Error> + Send + 'a>
 	where
-		P: 'a + Eq + Clone,
-		V: 'a + Hash + Eq,
-		I: 'a + Stream<Item=LocalizedMessage<P, V>>,
-		O: 'a + Sink<SinkItem=Message<P>,SinkError=I::Error>,
+		P: 'a + Send + Eq + Clone,
+		V: 'a + Send + Hash + Eq,
+		I: 'a + Send + Stream<Item=LocalizedMessage<P, V>>,
+		O: 'a + Send + Sink<SinkItem=Message<P>,SinkError=I::Error>,
+		I::Error: Send
 {
 	let prepared = HashSet::new();
 
@@ -90,3 +91,111 @@ pub fn agree<'a, P, I, O, V>(local_proposal: P, input: I, output: O, max_faulty:
 
 	Box::new(broadcast_message.and_then(move |_| wait_for_prepares))
 }
+
+#[cfg(test)]
+mod tests {
+	use futures::{Future, Stream, Sink};
+	use super::*;
+
+	#[test]
+	fn broadcasts_message() {
+		let (i_tx, i_rx) = ::futures::sync::mpsc::channel::<LocalizedMessage<usize, usize>>(10);
+		let (o_tx, o_rx) = ::futures::sync::mpsc::channel(10);
+		let max_faulty = 3;
+
+		let agreement = agree(
+			100_000,
+			i_rx.map_err(|_| ()),
+			o_tx.sink_map_err(|_| ()),
+			max_faulty,
+		);
+
+		::std::thread::spawn(move || {
+			let _i_tx = i_tx;
+			let _ = agreement.wait();
+		});
+
+		let sent_message = o_rx.wait()
+			.next()
+			.expect("to have a next item")
+			.expect("not to have an error");
+		let Message::Prepare(p) = sent_message;
+
+		assert_eq!(p, 100_000);
+	}
+
+	#[test]
+	fn concludes_on_2f_prepares() {
+		let (i_tx, i_rx) = ::futures::sync::mpsc::channel(10);
+		let (o_tx, _o_rx) = ::futures::sync::mpsc::channel(10);
+		let (timeout_tx, timeout_rx) = ::futures::sync::oneshot::channel();
+		let max_faulty = 3;
+
+		let agreement = agree(
+			100_000,
+			i_rx.map_err(|_| ()),
+			o_tx.sink_map_err(|_| ()),
+			max_faulty,
+		);
+
+		let iter = (0..(max_faulty * 2)).map(|i| {
+			LocalizedMessage {
+				message: Message::Prepare(100_000),
+				sender: i,
+			}
+		});
+
+		let (_i_tx, _) = i_tx.send_all(::futures::stream::iter_ok(iter)).wait().unwrap();
+
+		::std::thread::spawn(move || {
+			::std::thread::sleep(::std::time::Duration::from_secs(5));
+			timeout_tx.send(None).unwrap();
+		});
+
+		let agreed_value = agreement.map(Some).select(timeout_rx.map_err(|_| ()))
+			.wait()
+			.map(|(r, _)| r)
+			.map_err(|(e, _)| e)
+			.expect("not to have an error")
+			.expect("not to fail to agree");
+
+		assert_eq!(agreed_value, 100_000);
+	}
+
+	#[test]
+	fn never_concludes_on_less_than_2f_prepares() {
+		let (i_tx, i_rx) = ::futures::sync::mpsc::channel(10);
+		let (o_tx, _o_rx) = ::futures::sync::mpsc::channel(10);
+		let (timeout_tx, timeout_rx) = ::futures::sync::oneshot::channel();
+		let max_faulty = 3;
+
+		let agreement = agree(
+			100_000,
+			i_rx.map_err(|_| ()),
+			o_tx.sink_map_err(|_| ()),
+			max_faulty,
+		);
+
+		let iter = (1..(max_faulty * 2)).map(|i| {
+			LocalizedMessage {
+				message: Message::Prepare(100_000),
+				sender: i,
+			}
+		});
+
+		let (_i_tx, _) = i_tx.send_all(::futures::stream::iter_ok(iter)).wait().unwrap();
+
+		::std::thread::spawn(move || {
+			::std::thread::sleep(::std::time::Duration::from_millis(250));
+			timeout_tx.send(None).unwrap();
+		});
+
+		let agreed_value = agreement.map(Some).select(timeout_rx.map_err(|_| ()))
+			.wait()
+			.map(|(r, _)| r)
+			.map_err(|(e, _)| e)
+			.expect("not to have an error");
+
+		assert!(agreed_value.is_none());
+	}
+}