Implement tests for sharded mode

[andrewgodwin]

Right now, the tests only cover single-host mode; it would be nice to have proper tests for sharded mode as it's the easiest one to get wrong.

[b-thebest]

I can start working on this issue, I have experience of working with python of 1+year. I want to contribute in open source.
Please share me the doc and assign me the task