implement client ping (#108)

tests/client.rs

@@ -3,6 +3,28 @@ use std::net::SocketAddr;
 use tokio::net::TcpListener;
 use tokio::task::JoinHandle;
 
+/// A PING PONG test without message provided.
+/// It should return "PONG".
+#[tokio::test]
+async fn ping_pong_without_message() {
+    let (addr, _) = start_server().await;
+    let mut client = client::connect(addr).await.unwrap();
+
+    let pong = client.ping(None).await.unwrap();
+    assert_eq!(b"PONG", &pong[..]);
+}
+
+/// A PING PONG test with message provided.
+/// It should return the message.
+#[tokio::test]
+async fn ping_pong_with_message() {
+    let (addr, _) = start_server().await;
+    let mut client = client::connect(addr).await.unwrap();
+
+    let pong = client.ping(Some("你好世界".to_string())).await.unwrap();
+    assert_eq!("你好世界".as_bytes(), &pong[..]);
+}
+
 /// A basic "hello world" style test. A server instance is started in a
 /// background task. A client instance is then established and set and get
 /// commands are sent to the server. The response is then evaluated