Unit Test Pyodbc Database Connection

I wrote the following unit test to test whether the connection has been successfully established or not.

import unittest
from databse_access_pyodbc import *
from pyodbc import OperationalError


class TestDatabseConnection(unittest.TestCase):

    def test_connection_db(self):
        try:
            db_connection = get_db_connection()
        except OperationalError as err:
            self.fail(
                "get_db_connection() raised pyodbc.OperationalError. " +
                "Connection to database failed. Detailed error message: " + err)
        self.assertIsNone(db_connection)


if __name__ == '__main__':
    unittest.main()

If the connection can be established, the test says:

Ran 1 test in 0.001s

OK

Process finished with exit code 0

In case the connection could not be established, I'll get the following:

Traceback (most recent call last):
  File "xxx\PyCharm-P\ch-0\182.4505.26\helpers\pycharm\_jb_unittest_runner.py", line 35, in <module>
    main(argv=args, module=None, testRunner=unittestpy.TeamcityTestRunner, buffer=not JB_DISABLE_BUFFERING)
  File "xxx\Python36\lib\unittest\main.py", line 94, in __init__
    self.parseArgs(argv)
  File "xxx\Python36\lib\unittest\main.py", line 141, in parseArgs
    self.createTests()
  File "xxx\Python36\lib\unittest\main.py", line 148, in createTests
    self.module)
  File "xxx\Python36\lib\unittest\loader.py", line 219, in loadTestsFromNames
    suites = [self.loadTestsFromName(name, module) for name in names]
  File "xxx\Python36\lib\unittest\loader.py", line 219, in <listcomp>
    suites = [self.loadTestsFromName(name, module) for name in names]
  File "xxx\Python36\lib\unittest\loader.py", line 153, in loadTestsFromName
    module = __import__(module_name)
  File "xxx\tests\test_database_access_pyodbc.py", line 2, in <module>
    from databse_access_pyodbc import *
  File "xxx\databse_access_pyodbc.py", line 40, in <module>
    get_db_connection()
  File "xxx\databse_access_pyodbc.py", line 36, in get_db_connection
    autocommit=True)
pyodbc.OperationalError: ('08001', '[08001] [Microsoft][ODBC Driver 11 for SQL Server]Named Pipes-Anbieter: Es konnte keine Verbindung zu SQL Server hergestellt werden [53].  (53) (SQLDriverConnect); [08001] [Microsoft][ODBC Driver 11 for SQL Server]Anmeldungstimeout abgelaufen (0); [08001] [Microsoft][ODBC Driver 11 for SQL Server]Netzwerkbezogener oder instanzspezifischer Fehler beim Herstellen einer Verbindung mit SQL Server. Der Server wurde nicht gefunden, oder auf ihn kann nicht zugegriffen werden. Überprüfen Sie, ob der Instanzname richtig ist und ob SQL Server Remoteverbindungen zulässt. Weitere Informationen erhalten Sie in der SQL Server-Onlinedokumentation. (53)')

Process finished with exit code 1
Empty test suite.

Why is the exception OperationalError not catched by the test case and why does it say: Empty test suite?

from Unit Test Pyodbc Database Connection