Add Test for IPacket & PacketIdAttribute

Server.Tests/PacketTests.cs

@@ -0,0 +1,18 @@
+using System.Reflection;
+
+namespace Server.Tests;
+
+public class PacketTests
+{
+	[Fact]
+	public void TestPacketInheritingIPacket()
+	{
+		var allTypes = AppDomain.CurrentDomain.GetAssemblies().SelectMany(x => x.GetTypes())
+			.Where(x => x.IsAssignableTo(typeof(Server.Packets.IPacket)) && x.IsClass);
+		if (!allTypes.Any())
+			true.Should().BeTrue("There have been no types found which can be checked");
+		else
+			allTypes.All(t => t.GetCustomAttributes<Server.Packets.PacketIdAttribute>().Any())
+				.Should().BeTrue("All types inheriting from IPacket should have the PacketIdAttribute attribute.");
+	}
+}