How to test dockered Flask-Cognito microservice?

I need test dockered Flask-Cognito application.

My requirements are:

• Test running docker container as a blackbox.
• It means test only Flask endpoints.
• I would like avoid some changes in the code (during the testing). Best way is a emulate AWS Cognito service.
• OPTIONAL: I would like use tool Tavern! or something similar.

I am new in AWS so I will need answer for dummy ;).

I found emulators as a:

• vcrpy
• localstack
• moto

But I do not know how to use it.