fix: MessageSendingTests causing memory leak during editor tests. (Unity-Technologies#2125)

* fix

Seeing if this fixes the issue with our memory leaks.

* fix

minor fix to my fix.  Need to reconnect the client after creating the new MessagingSystem.
adjusted a comment.

* Update com.unity.netcode.gameobjects/Tests/Editor/Messaging/MessageSendingTests.cs

Adding Fatih's LF/CR suggestion for readability

Co-authored-by: Fatih Mar <mfatihmar@gmail.com>

Co-authored-by: Fatih Mar <mfatihmar@gmail.com>

Author: 2 people

com.unity.netcode.gameobjects/Tests/Editor/Messaging/MessageSendingTests.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Text.RegularExpressions;
 using NUnit.Framework;
@@ -43,21 +44,38 @@ public void Send(ulong clientId, NetworkDelivery delivery, FastBufferWriter batc
             }
         }
 
-        private class TestMessageProvider : IMessageProvider
+        private class TestMessageProvider : IMessageProvider, IDisposable
         {
+            // Keep track of what we sent
+            private List<List<MessagingSystem.MessageWithHandler>> m_CachedMessages = new List<List<MessagingSystem.MessageWithHandler>>();
+
+            public void Dispose()
+            {
+                foreach (var cachedItem in m_CachedMessages)
+                {
+                    // Clear out any references to MessagingSystem.MessageWithHandlers
+                    cachedItem.Clear();
+                }
+                m_CachedMessages.Clear();
+            }
+
             public List<MessagingSystem.MessageWithHandler> GetMessages()
             {
-                return new List<MessagingSystem.MessageWithHandler>
+                var messageList = new List<MessagingSystem.MessageWithHandler>
                 {
                     new MessagingSystem.MessageWithHandler
                     {
                         MessageType = typeof(TestMessage),
                         Handler = MessagingSystem.ReceiveMessage<TestMessage>
                     }
                 };
+                // Track messages sent
+                m_CachedMessages.Add(messageList);
+                return messageList;
             }
         }
 
+        private TestMessageProvider m_TestMessageProvider;
         private TestMessageSender m_MessageSender;
         private MessagingSystem m_MessagingSystem;
         private ulong[] m_Clients = { 0 };
@@ -66,15 +84,16 @@ private class TestMessageProvider : IMessageProvider
         public void SetUp()
         {
             TestMessage.Serialized = false;
-
             m_MessageSender = new TestMessageSender();
-            m_MessagingSystem = new MessagingSystem(m_MessageSender, this, new TestMessageProvider());
+            m_TestMessageProvider = new TestMessageProvider();
+            m_MessagingSystem = new MessagingSystem(m_MessageSender, this, m_TestMessageProvider);
             m_MessagingSystem.ClientConnected(0);
         }
 
         [TearDown]
         public void TearDown()
         {
+            m_TestMessageProvider.Dispose();
             m_MessagingSystem.Dispose();
         }
 
@@ -246,7 +265,16 @@ private class TestNoHandlerMessageProvider : IMessageProvider
         [Test]
         public void WhenReceivingAMessageWithoutAHandler_ExceptionIsLogged()
         {
+            // If a MessagingSystem already exists then dispose of it before creating a new MessagingSystem (otherwise memory leak)
+            if (m_MessagingSystem != null)
+            {
+                m_MessagingSystem.Dispose();
+                m_MessagingSystem = null;
+            }
+
+            // Since m_MessagingSystem is disposed during teardown we don't need to worry about that here.
             m_MessagingSystem = new MessagingSystem(new NopMessageSender(), this, new TestNoHandlerMessageProvider());
+            m_MessagingSystem.ClientConnected(0);
 
             var messageHeader = new MessageHeader
             {