How to join a server?

I had some trouble with this as well. What you need to do is:

1. Go to the Discord developer pages (login if you haven't).
2. Go to the application with the bot you want to add to your channel.
3. Copy the Client/Application ID.
4. Go to https://discordapp.com/oauth2/authorize?client_id=CLIENT_ID_GOES_HERE&scope=bot&permissions=0 < You can set permissions for the bot here. Permissions can be calculated here.
5. Select server and click authorize.

Your bot will now be a member of the server and will respond to commands you give it. Ex. !test in the code you have given.

EDIT: You can now use the permissions link (1) to generate the entire URL needed.

It's been 4 years since I asked the question and here's how I deal with this problem nowadays.

I use https://discordapi.com/permissions.html where you just paste your bot's ID (which you can get here: https://discord.com/developers/applications ) and it also has the benefit of calculating whatever permissions configuration you want for you.

If you're lazy, this could be a decent solution for you too.

I suggest editing the code like this:

    @client.event
async def on_ready():
    print('Logged in as')
    print(client.user.name)
    print(client.user.id)
    print('Invite: https://discordapp.com/oauth2/authorize?client_id={}&scope=bot'.format(client.user.id))
    print('------')

I think this is the best and easiest solution. It works for me.

EDIT: Discord actually made their own OAuth2 url generator, so use that: https://discordapp.com/developers/tools/oauth2-url-generator