Question

I have a data structure that is created in one function and passed onto other functions. I am trying to unit test all those functions.

Do I need to re-create that data structure (the environment) at each function? I tried using a global variable but I cannot guarantee which test case will run before the other.

I know I cannot override __init__ of unittest.TestCase without much headache.

How else can I achieve that? Passing a parameter or somehow making it a variable and avoiding a race condition?

Answer 1

It sounds like you do not want to redefine the data structure before each test. As long as the tests do not modify the data, I don’t think there is any problem with defining the data structure in __init__:

import unittest

class Test(unittest.TestCase):
    def __init__(self, methodName = 'runTest'):
        unittest.TestCase.__init__(self, methodName)
        self.data = range(5)

    def test_getitem(self):
        self.assertEqual(self.data[1],1)

    def test_reversed(self):
        self.assertEqual(list(reversed(self.data)),[4,3,2,1,0])

if __name__ == '__main__':
    import sys
    sys.argv.insert(1,'--verbose')
    unittest.main(argv = sys.argv)

yields

% test.py
test_getitem (__main__.Test) ... ok
test_reversed (__main__.Test) ... ok

----------------------------------------------------------------------
Ran 2 tests in 0.000s

OK