Fails with ` pytest -n $(nproc --all)`

[keremsahn]

def test09_templated_function(self):
        """Templated free function"""
    
        import cppjit
    
>       mul = cppjit.gbl.multiply
              ^^^^^^^^^^^^^^^^^^^
E       AttributeError: <namespace cppjit.gbl at 0x2647e8b0> has no attribute 'multiply'. Full details:
E         type object '' has no attribute 'multiply'
E         'multiply' is not a known C++ class
E         'multiply' is not a known C++ template
E         'multiply' is not a known C++ enum

test/test_doc_features.py:717: AttributeError

Reason: multiply is defined at class TestDOCFEATURES, but test09 is at class TestTUTORIALFEATURES

2. Same for test_lowlevel.py::TestLOWLEVEL::test03_memory : AttributeError: module 'cppjit' has no attribute 'll'
   The ll is not directly included at test03, and when test03 runs before one of the tests that import ll finishes, test fails

[Vipul-Cariappa]

I suspect this is a pytest bug, or maybe it is expected behaviour of pytest, and we should update the test...
As I understand it, setup_class needs to run before the test itself, but when running tests individually, setup_class is not run. I guess when running in parallel, something similar happens.
Can you also test my hypothesis about setup_class, and check pytest's documentation about it?

For cppjit.ll, can you add import cppjit.ll at the start of the test, or in setup_class? Check if that solves the problem.