Add test cases for async function calls

[gagb]

          > > To test I created a sample notebook two agents and a group chat. The notebook worked. I can upload the example to `notebooks/` in a different PR if its useful.

The reason to have tests is to ensure code coverage in CI. Notebooks are good for a different purpose. They can't replace tests unless they are included in the tests.

Sounds good, I will contribute a test case in a different PR (see async-test branch) :) Thanks @victordibia for helping with it.

Originally posted by @gagb in #87 (comment)