pytest: test for import of subpackage

Question

I want to do the following. In my project a I have a factory class Fac with instance fac=Fac() , where certain classes register to. These classes reside in a subpackage ab .

If I do a plain import a , the subpackage ab is not imported, no classes are registered, and thus fac.registered_classes is an empty list.

After an import of subpackage b fac.registered_classes gets filled with the classes in subpackage b .

To not confuse the user, I added the line

import .b in the __init__.py of package a .

Now, I'd like to write a test with pytest that basically passes, if the fac.registered_classes is not empty; so noone accidentally erases that line in my __init__.py . Lets call that test test_import_b

Different tests of course also test functionality of subpackage b , thus importing b themselves explicitly.

However, it seems that all imports during test runs are available for all tests. While just running the single test test_import_b fails if the import line is removed in __init__.py , it does not anymore if all tests are ran simultaneously.

What am I supposed to do, to make my test setup work?

Answer 1

This is correct py.test and Python behavior. Module body level code is run when to module is imported. Python virtual machine maintains imported modules per-process.

I do not believe there is a good solution to achieve the behavior you want. Two strategies come to my mind

• Do not ever register anything implicitly on module import only - make registering everything explicit through a function call like having your init()

• In the tests that explicitly need to import and have register run, import it at the beginning of the test or make a fixture that does the import

Eg

def test_boohoo():
     import a.b
     # Test goes here