themattrix/python-simian

A decorator for easily mocking out multiple dependencies by monkey-patching.

Simian

A decorator for easily mocking out multiple dependencies by monkey-patching.

@simian.patch(module=..., external=[...], internal=[...])

Installation:

$ pip install simian

simian.patch is a convenience wrapper around mock.patch with the following benefits:

1. All patched objects are collected under a single master_mock, which is provided to the function being decorated. Any patched target can be accessed by its basename (e.g., a patched time.sleep would be accessed in the decorated function as master_mock.sleep).
2. The patching works even if the target is imported directly (e.g., a call to sleep is patched the same as a call to time.sleep). Simian handles this by reloading the module under test after applying the external patches.
3. Objects internal to the module under test can be patched as well. They are collected under the same master_mock and can be referenced in the same way.

After leaving the decorated function, simian reloads the module under test again, bringing it back to its pre-patched state (although all of the module's addresses in memory have changed).

External Patching

#
# my_package.my_module
#

from time import sleep


def my_sleep(duration_secs):
    print('Sleeping for {n} seconds'.format(n=duration_secs))
    sleep(duration_secs)


#
# my_package.test.test_my_module
#

import simian
from my_package import my_module


@simian.patch(my_module, external=['time.sleep'])
def test_my_sleep(master_mock):
    my_module.my_sleep(99)
    master_mock.sleep.assert_called_once_with(99)

Internal Patching

The above example demonstrates external patching, but internal (same-module) patching works as well. Let's extend the above example.

#
# my_package.my_module
#

from time import sleep


def my_sleep(duration_secs):
    my_logger('Starting {n}-second sleep'.format(n=duration_secs))
    sleep(duration_secs)
    my_logger('Finished {n}-second sleep'.format(n=duration_secs))


def my_logger(msg):
    print(msg)


#
# my_package.test.test_my_module
#

import simian
from mock import call
from my_package import my_module


@simian.patch(my_module, external=['time.sleep'], internal=['my_logger'])
def test_my_sleep(master_mock):
    my_module.my_sleep(99)
    master_mock.assert_has_calls(
        calls=[
            call.my_logger('Starting 99-second sleep'),
            call.sleep(99),
            call.my_logger('Finished 99-second sleep')],
        any_order=False)