Mocking sqlalchemy.create_engine fails to mock the function - sqlalchemy

Question

I want to test my DBConnect class, which manages and returns connections made with sqlalchemy.
I want to specifically test that the constructor of DBConnect calls sqlalchemy.create_engine and stores the engine in the connection.
My test function is this:
from unittest import mock
from catcom.db_connect import DBConnect
import os
class MockEngine:
def connect(self):
return "test_connection"
#mock.patch("sqlalchemy.create_engine", return_value=MockEngine())
def test_from_key_uses_correct_key(mock):
print(mock)
db = DBConnect("user", "pw", "127.0.0.1", "1234", "db")
assert db.connection == "test_connection"
However, I see a response of:
E sqlalchemy.exc.OperationalError: (psycopg2.OperationalError) connection to server at "127.0.0.1", port 1234 failed: Connection refused
E Is the server running on that host and accepting TCP/IP connections?
How can I mock the create_engine method without it being actually called?
UPDATE
Adding the DB Connect class and relevant methods.
from sqlalchemy import create_engine
import os
class DBConnect:
"""Manages database connection using SQLalchemy"""
def __init__(self, user: str, password: str, host: str, port: str, database: str):
self.user = user
self.password = password
self.host = host
self.port = port
self.database = database
self.connection = self.connect()
def connect(self):
"""creates a connection object that is used to query database using SQLalchemy core
automatically created in __init__"""
engine = create_engine(
f"postgresql+psycopg2://{self.user}:{self.password}#{self.host}:{self.port}/{self.database}"
)
return engine.connect()

Answer 1

You are importing create_engine out of the sqlalchemy namespace with from sqlalchemy import create_engine, which puts it in the module's namespace.
That's what you need to patch, see where to patch.
#mock.patch('catcom.db_connect.create_engine', return_value='test_success')
Although, patching catcom.db_connect.create_engine to return 'test_success' will cause a problem when the DBConnect.connect method tries to call the connect method of the engine (which will be a string).