Added some TCP wrapper classes for testability

AMWD.Protocols.Modbus.Tcp/Extensions/StreamExtensions.cs

@@ -1,5 +1,6 @@
 using System.Threading;
 using System.Threading.Tasks;
+using AMWD.Protocols.Modbus.Tcp.Utils;
 
 namespace System.IO
 {
@@ -22,5 +23,23 @@ namespace System.IO
 			cancellationToken.ThrowIfCancellationRequested();
 			return buffer;
 		}
+
+		public static async Task<byte[]> ReadExpectedBytesAsync(this NetworkStreamWrapper stream, int expectedBytes, CancellationToken cancellationToken = default)
+		{
+			byte[] buffer = new byte[expectedBytes];
+			int offset = 0;
+			do
+			{
+				int count = await stream.ReadAsync(buffer, offset, expectedBytes - offset, cancellationToken);
+				if (count < 1)
+					throw new EndOfStreamException();
+
+				offset += count;
+			}
+			while (offset < expectedBytes && !cancellationToken.IsCancellationRequested);
+
+			cancellationToken.ThrowIfCancellationRequested();
+			return buffer;
+		}
 	}
 }