Mock returning an ImportError when patching a module that's imported

Question

I'm having some trouble mocking a function. Said function is imported and used in run_parsers.py and I'm getting

ImportError: 'No module named run_parsers'

When I'm attempting to mock.patch run_parsers.py .

Here's my test code in test_run_parsers.py

from .. import run_parsers # Used in all my other tests.

def test_node_data_parser_throws_exception(self):
    def parser():
        return NotImplementedError()

    with mock.patch("run_parsers.get_node_paths") as node_paths:
        node_paths.return_value = "node_1"
        run_parsers.get_node_data(parser, "/a/path")

Here's my repository structure

control_scripts
├── __init__.py
├── README.md
├── run_all_parsers.py
├── run_parsers.py
└── tests
    ├── __init__.py
    ├── test_run_parsers.py

According to this tutorial I'm supposed to mock where the function is imported. This is why I'm attempting to mock the calling module rather than the module that defines get_node_paths

Answer 1

I'm not sure if this duplicates your setup exactly, but here is a simple test case that worked for me.

The directory setup is:

c:\work
    \control
        __init__.py
        scripts.py
        \tests
            __inti__.py
            mytests.py

and c:\work is on sys.path

In the module scripts.py:

def identity(x):
    return x

def do_identity(x):
    return identity(x)

In mytests.py:

import unittest
from unittest.mock import patch
from control import scripts

class MyTest(unittest.TestCase):

    def test_patch(self):

        with patch('control.scripts.identity') as mymock:
            mymock.return_value = 99
            self.assertEqual(scripts.do_identity(1), 99)

    def test_no_patch(self):

            self.assertEqual(scripts.do_identity(1), 1)            

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

So what I am trying to do here is to mock the function 'identity' which is called by the function 'do_identity'. Both functions are in the 'scripts' module. This test runs with no errors or failures.

And I can run this from any directory as:

c:\any_directory> python c:\work\control\tests\mytests.py

Answer 2

For more complicated project structure (or if you want to make te mock parts shorter), I come up with a tricky solution, because I needed a seperation between the Logic and the UI.

My structure looks something like this:

├───sourceroot
│   ├───python_pkg
│   │   ├───__init__
│   │   └───subpkg
│   │       ├───__init__
│   │       ├───logic
│   │       │   ├───lpkg1
│   │       │   │   ├───__init__
│   │       │   │   ├───file1.py
│   │       │   │   └───file2.py
│   │       │   ├───lpkg2
│   │       │   │   ├───__init__
│   │       │   │   ├───file3.py
│   │       │   │   └───file4.py
│   │       │   ├───__init__
│   │       │   └───file.py
│   │       └───ui
│   │           ├───uipkg3
│   │           │   ├───__init__
│   │           │   ├───file_ui1.py
│   │           │   └───file_ui2.py
│   │           ├───uipkg4
│   │           │   ├───__init__
│   │           │   ├───file_ui3.py
│   │           │   └───file_ui4.py
│   │           ├───__init__
│   │           └───file_ui.py
│   └───packages
│       └───some_3rd_party_packages
├───srcfiles_from_3rd_parties
└───tests
    └───unit_tests_py
        ├───__init__
        └───test.py

I had to reference on the file.py and file1.py from test.py. To see the sourceroot from the test.py-file I write the following into the sourceroot/tests/unit_test_py/__init__

import sys
import os
sys.path.append(os.path.realpath(os.path.join(os.path.dirname(__file__), '..', '..')))

After the Initialisation and adding the sourceroot to the paths (where Python will look up) the test.py class is ready to Edit:

Before:

import mock
from sourceroot.python_pkg.subpkg.logic import file
from sourceroot.python_pkg.subpkg.logic.lpkg1.file1 import SomeClassFromFile1 as SCF1

class Test_test1(object):
    def test_first(self, mocker):
        mocker.patch('sourceroot.python_pkg.subpkg.logic.lpkg1.file1.some_function_which_SCF1_calls')
        mocker.patch('sourceroot.python_pkg.subpkg.logic.file.SomeClassInFile.some_function_which_SomeClassInFile_calls')
        SCF1.some_function_in_SCF1()
        expected_information = True
        assert SCF1.is_something() == expected_information

After:

import mock
from sourceroot.python_pkg.subpkg.logic import file
from sourceroot.python_pkg.subpkg.logic.lpkg1.file1 import SomeClassFromFile1 as SCF1

class Test_test1(object):
    def test_first(self, mocker):
        mocker.patch.object(SCF1, 'some_function_which_SCF1_calls')
        mocker.patch.object(file.SomeClassInFile, 'some_function_which_SomeClassInFile_calls')
        SCF1.some_function_in_SCF1()
        expected_information = True
        assert SCF1.is_something() == expected_information