I have a problem with calling the command in extension. For example, I try to do it in the following way:

//...
namespace Oxide.Ext.Tests
{
    class TestSystem : CSPlugin
    {
        private readonly Command cmd = Interface.Oxide.GetLibrary<Command>();
		
        public override void HandleAddedToManager(PluginManager manager)
        {
            cmd.AddConsoleCommand("cmdtestconsole", this, "CmdTest");
            cmd.AddChatCommand("cmdtest", this, "CmdTest");

            base.HandleAddedToManager(manager);
            Interface.Oxide.LogInfo("[Test] HandleAddedToManager");
        }
		
        private void CmdTest(PlayerSession session, string command, string[] args)
        {
            Interface.Oxide.LogInfo("[Test] CmdTest");
        }
        private void CmdTest(IPlayer player, string command, string[] args)
        {
            Interface.Oxide.LogInfo("[Test] CmdTest");
        }
        private void CmdTest(string command, string[] args)
        {
            Interface.Oxide.LogInfo("[Test] CmdTest");
        }
	}
}
​

I see a message "[Test] HandleAddedToManager" after starting the server with this ext. When I call the chat command or console command I do not receive the "command does not exist" message, but I also do not get any messages from the console coming from this plugin.

I'm doing something incorrectly?

try calling

base.HandleAddedToManager(manager);​

first

Here is a working example of registering a command: https://github.com/theumod/uMod.Rust/blob/oxide/src/RustCore.cs#L74-L88

You can use the cmd method and game-specific handling that you are using, but using something such as HandleAddedToManager is definitely an atyipcal way of handling it.

Thank @Wulf, working properly.