Add pytest-asyncio unit tests

[timsaucer]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

This is a follow on to #975 where we want to add unit tests but we need to add in a dependency. We should do this after completing #977 rather than do the work twice.

Describe the solution you'd like

Add unit tests. See PR #975 for details.

Describe alternatives you've considered

None