Make sure tests are failing when exception is thrown

[gawi151]

Is your feature request related to a problem? Please describe. Make sure tests using common_tests.dart are failing properly.

Describe the solution you'd like All common test functions should properly await and return Future in common_tests.dart. Encountered problems when changing test in https://github.com/nomtek/mistralai_client_dart/pull/51

Describe alternatives you've considered n/a

Additional context

• found during review of https://github.com/nomtek/mistralai_client_dart/pull/51