python: mock a module

Question

Is it possible to mock a module in python using unittest.mock? I have a module named config, while running tests I want to mock it by another modul

Answer 1

Consider this following setup

configuration.py:

import os

class Config(object):
    CONF_VAR1 = "VAR1"
    CONF_VAR2 = "VAR2"

class TestConfig(object):
    CONF_VAR1 = "test_VAR1"
    CONF_VAR2 = "test_VAR2"


if os.getenv("TEST"):
    config = TestConfig
else:
    config = Config

now everywhere else in your code you can use:

from configuration import config
print config.CONF_VAR1, config.CONF_VAR2

And when you want to mock your coniguration file just set the environment variable "TEST".

Extra credit: If you have lots of configuration variables that are shared between your testing and non-testing code, then you can derive TestConfig from Config and simply overwrite the variables that need changing:

class Config(object):
    CONF_VAR1 = "VAR1"
    CONF_VAR2 = "VAR2"
    CONF_VAR3 = "VAR3"

class TestConfig(Config):
    CONF_VAR2 = "test_VAR2"
    # CONF_VAR1, CONF_VAR3 remain unchanged