Add some unit test to the app

The app has no automated test at the moment. There have been at least one error that would be catched by a unit test (2332ab28). For the easy cases a unit test should be implemented. https://docs.flutter.dev/cookbook/testing/unit/introduction

• Upload of a trip
• Computing min distance of a segment
• Creation and deletion of a trip in Database
• Ivalid ble data
• If in privacy zone do not record a segement