How do I check if code is being run from a nose-test?

Question

I have some code which is used in a unit test. However, the library it loads requires some data which isn't actually required for the nose-test, because that data is mocked out by the unit test. I'd like to protect the file-reads in the library so that they don't get called in the case of a nose test.

Is there an easy way to do this?

I can probably do something with sys.modules, or the initial command line, but I'd prefer something more elegant, if it exists.

how about checking if some file exists, if it doesn't, then flag the code as 'nose-test' and prevent the load of such files. — tglaria, Jan 04 '16 at 19:47
I don't understand - if it's mocked out, why are the reads still happening? Could you provide a [mcve]? — jonrsharpe, Jan 04 '16 at 19:49
I can't really give an example better than "in the unit-test case I want to exclude this code" The reason it's happening is that I need a class from a library, so I'm importing the library. That library is where the data is normally read, so the reads are there, but I don't actually need them to take place in the unit test case. — Brian Postow, Jan 04 '16 at 19:54
@BrianPostow: You shouldn't have to modify your code because of your tests. If you feel like you have to, it might suggest your design is bad. — Vincent Savard, Jan 04 '16 at 19:55
Oh, the design is HORRIBLE. But I can't re-arrange the code until I have tests that confirm that when I re-arrange things I haven't broken anything. — Brian Postow, Jan 04 '16 at 19:56
Having just typed that, I realize that eventually, after I refactor, hopefully the entire problem will go away, so maybe just doing something stupid with sys.modules is the best way. Leave it ugly, so that I fix ALL of it later... — Brian Postow, Jan 04 '16 at 19:57
Too much work. eventually, I should factor out the parts that are relevant to tests into a library and data reading into a different place, but for now... meh. — Brian Postow, Jan 04 '16 at 20:04
Instead of making your code aware of being under test or not..either mock the functionality and/or make your code composable to accept the objects to use so they can be mocked in tests. For mocking built-in functions like `open` you may check http://stackoverflow.com/questions/1289894/how-do-i-mock-an-open-used-in-a-with-statement-using-the-mock-framework-in-pyth — Montaro, Feb 06 '17 at 13:17
This question is related: https://stackoverflow.com/questions/7341005/python-conditional-variables-based-on-whether-nosetest-is-running — Amos Egel, Nov 01 '19 at 21:56

score 10 · Answer 1 · answered Jan 04 '16 at 20:08

As mentioned in comments, the structure of this code is a mess, and part of the point of the tests is to make sure that I don't break things when I refactor...

So, for now, (unless someone gives me a better answer), I'm using:

if 'nose' not in sys.modules.keys():
    <read the data>

score 2 · Answer 2 · answered Jan 04 '16 at 20:03

Correct approach would be to mock all code with side-effects (I'll assume that what you do not want) with empty mocks.

Given tested_module my_module:

def do_something_and_destroy_world():
    destroy_world()
    return None

Sample test file is:

import mock
import unittest

import my_module

class MyTest(unittest.TestCase):
    def testSomethingUgly(self):
        with mock.patch('my_module.destroy_world', return_value=None):
            result = do_something_and_destroy_world()
            self.assertIsNone(result)

When tests are run, assertion will be correct, and destroy_world wouldn't be called - instead it'll get replaced with empty mock with fixed return value.

Nice. I don't think it would work as nicely in my current code because the messy code isn't actually in a method. Unless I can do a with mock.patch around an import, and even then it would get messy... But it's good to know what the right way to do this is in sane code... — Brian Postow, Jan 04 '16 at 20:14

How do I check if code is being run from a nose-test?

2 Answers2