Issue Type: Bug

Here is a sample test script in which the same test is executed with different configurations.

import unittest

class Foo(unittest.TestCase):
    config = "Hello"
    def test_Print(self):
        print(self.config)

class FooConfigured(Foo):
    config = "World"

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

If I try to run all tests in the file, only FooConfigured is executed. If I try to run the Foo class as a whole, the same thing happens. I have to explicitly run Foo.test_Print or it will never be executed.

In my real world project there are 15 test methods, and the configuration required is picking a version of a dependency to run against.

Extension version: 2019.11.50794
VS Code version: Code 1.40.1 (8795a9889db74563ddd43eb0a897a2384129a619, 2019-11-13T16:49:30.162Z)
OS version: Linux x64 4.15.0-70-generic