How to Resolve RuntimeError: Working Outside of Application Context in Flask Unit Tests?

RuntimeError: Working Outside of Application Context

Problem Statement:
When attempting unit testing on a Flask application, calling the 'before_request' function from outside of the application context raises a RuntimeError:

with patch('__main__.mysql.connector.connect') as mock_mysql_connector_connect:
  object = TestMySQL()
  object.before_request()  # Runtime error on calling this

Root Cause:
Flask uses an Application Context to manage request-specific data. When calling functions outside of this context, as in the unit test, the necessary resources are not available, leading to the aforementioned error.

Solution:
To resolve this issue, the unit test must be executed within the Application Context. This can be achieved using the 'app_context()' decorator:

def test_connection(self):
    with app.app_context():
        # Test code here

Alternatively, the 'app_context()' call can be encapsulated within a test setup method.

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