Mocking __init__() for unittesting

You should use mock package to mock the method __init__ of the class:

from mock import patch


def test_database_thing(self):
    def __init__(self, dbName, user, password):
        # do something else
    with patch.object(DatabaseThing, '__init__', __init__):
        # assert something

Instead of mocking, you could simply subclass the database class and test against that:

class TestingDatabaseThing(DatabaseThing):
     def __init__(self, connection):
          self.connection = connection

and instantiate that class instead of DatabaseThing for your tests. The methods are still the same, the behaviour will still be the same, but now all methods using self.connection use your test-supplied connection instead.