Add client test case

Client/Assets/Scripts/Test/NetworkConnectionTest.cs

@@ -0,0 +1,26 @@
+using System.Threading.Tasks;
+using Network;
+using UnityEngine;
+
+namespace Test
+{
+    public class NetworkConnectionTest : MonoBehaviour
+    {
+        private async void Start()
+        {
+            await BasicTest();
+        }
+
+        private static async Task BasicTest()
+        {
+            var result = await UnityTcpClient.Instance.Connect("127.0.0.1", 12345);
+            if (result) Debug.Log("Connected to server!");
+            else Debug.LogError("Failed to connect to server!");
+
+            string buffer = null;
+            while (buffer is null) buffer = await UnityTcpClient.Instance.Receive();
+
+            Debug.Log($"Received contents: {buffer}");
+        }
+    }
+}