The importing of classes using imp was tested with:

from unittest import TestCase

import os
import imp
import importer

class TestSource(TestCase):
    def test_import(self):
        """
        module `source` contains class `SourceCase` with attribute cow set to 'pie'
        """
        path = os.path.dirname(__file__)
        f, package, description = imp.find_module("source", [path])
        source = imp.load_module('source', f, package, description)
        SourceCase = getattr(source, "SourceCase")
        case_o = SourceCase()
        expected = importer.source.SourceCase()
        self.assertEqual(expected.cow, case_o.cow)

        # this won't work - using imp gets source.SourceCase, but import gets importer.source.SourceCase
        #self.assertIsInstance(case_o, source.SourceCase)
        return

    def test_subdirectory_import(self):
        """
        module `subsource` contains a class Subsource with attribute `apropos` set to 'nothing'
        """
        top = os.path.dirname(__file__)
        f, package_path, d = imp.find_module("subdir", [top])
        f, mod_path, description = imp.find_module('subsource', [package_path])
        subsource = imp.load_module('subdir.subsource', f, mod_path, description)
        Subsource = getattr(subsource, "Subsource")
        source_obj = Subsource()
        expected = importer.subdir.subsource.Subsource()
        self.assertEqual(expected.apropos, source_obj.apropos)
        return
# end class TestSource