* test: add unit tests in server
* test: add unit tests of app.py in server
* test: reformat the codes
* test: add more tests to cover the exception part
* test: add more tests on the server app part
* fix: don't show the detail exception to the client
* test: try to fix the CI test
* fix: keep the TTS API call without exposure information
* Fixed the unit test errors
* Fixed the lint error
