test.py

import discord
from botClient import client
from discord.ext import commands

class TestCog:
    def __init__(self, client):
        self.client = client

    async def on_message_delete(self, message):
        await message.channel.send(f"{message.author}'s message has been deleted.")

    @commands.command()
    async def ping(self, ctx):
        await ctx.send('Pong!')

def setup(client):
    client.add_cog(TestCog(client))