added the interface IWebSocket for easier mock up

src/WebSocket4Net/IWebSocket.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Buffers;
+using System.Threading;
+using System.Threading.Tasks;
+using SuperSocket.WebSocket;
+
+namespace WebSocket4Net
+{
+    public interface IWebSocket
+    {
+        ValueTask<bool> OpenAsync(CancellationToken cancellationToken = default);
+
+        ValueTask<WebSocketPackage> ReceiveAsync();
+
+        ValueTask SendAsync(string message);
+
+        ValueTask SendAsync(ReadOnlyMemory<byte> data);
+
+        ValueTask SendAsync(ref ReadOnlySequence<byte> sequence);
+
+        ValueTask CloseAsync(CloseReason closeReason, string message = null);
+    }
+}

src/WebSocket4Net/WebSocket.cs

@@ -18,7 +18,7 @@
 
 namespace WebSocket4Net
 {
-    public class WebSocket : EasyClient<WebSocketPackage>
+    public class WebSocket : EasyClient<WebSocketPackage>, IWebSocket
     {
         private static readonly Encoding _asciiEncoding = Encoding.ASCII;
         private static readonly Encoding _utf8Encoding = new UTF8Encoding(false);
@@ -294,11 +294,6 @@ public ValueTask SendAsync(ref ReadOnlySequence<byte> sequence)
             return SendAsync(_packageEncoder, package);
         }
 
-        public async ValueTask CloseAsync(CloseReason closeReason)
-        {
-            await CloseAsync(closeReason, string.Empty);
-        }
-
         private byte[] GetBuffer(int size)
         {
             return new byte[size];
@@ -309,7 +304,7 @@ public override async ValueTask CloseAsync()
             await CloseAsync(CloseReason.NormalClosure, string.Empty);
         }
 
-        public async ValueTask CloseAsync(CloseReason closeReason, string message)
+        public async ValueTask CloseAsync(CloseReason closeReason, string message = null)
         {
             var package = new WebSocketPackage();