Is your enhancement proposal related to a problem? Please describe.
The current babblesim tests for MCP mainly focuses on the case where everything goes right, and do not test much invalid behavior or error handling.

Describe the solution you'd like
All APIs should be tested with invalid values to verify that they will return an error.

To the extent possible, the APIs should also be used in cases where the the remote device should perform some error handling.

Finally the APIs should be tested with disconnects.

Describe alternatives you've considered
To test against a non-conforming device, some verification and checks in the stack needs to be disabled. TBD if this is a good idea to test somehow.

Additional context
N/A