🚸 Improve assertion error message if a group is not a valid subclass

[chrisburr]

With the latest typer release my CI (which runs a typer based script) started failing with:

Traceback (most recent call last):
  File "/builds/cburr/DIRAC/./integration_tests.py", line 750, in <module>
    app()
AssertionError

The cause turned out to be:

https://github.com/tiangolo/typer/blob/fac64ca03e9fda619710702c3364e233e0e644ac/typer/main.py#L505

which was triggered by my script contianing:

class NaturalOrderGroup(click.Group):
    """Group for showing subcommands in the correct order"""

    def list_commands(self, ctx):
        return self.commands.keys()

The fix is easy and just requires replacing click.Group with typer.core.TyperGroup however I think the assertion error should be made this clearer.

[github-actions]

📝 Docs preview for commit ec50f29 at: https://639cea38fceb140981a7fdf5--typertiangolo.netlify.app

[svlandeg]

It's a good idea to add this message to help developers with debugging. Thanks for your contribution!

[tiangolo]

Nice, thank you @chrisburr! 🚀