Add extra tests for non-None-ness in test_classes

Some weird errors are happening in tests, where the image, or
image.pixels, is None. So, we assert that both are not None so that
tests fail rather than error out.

 Changes to be committed:
	modified:   tests/test_classes.py

tests/test_classes.py

@@ -236,9 +236,11 @@ def test_iter_by_files(self):
         res = ts.iter_by_files()
         self.assertTrue(isgenerator(res))
         for iii, image in enumerate(res):
+            self.assertIsNot(image, None)
             self.assertEqual(image.path, helpers.TS_FILES_JPG[iii])
             self.assertEqual(image.datetime,
                              helpers.TS_DATES_PARSED[iii])
+            self.assertIsNot(image.pixels, None)
             self.assertEqual(image.pixels.dtype, helpers.TS_JPG_DTYPE)
             self.assertEqual(image.pixels.shape, helpers.TS_JPG_SHAPE)
 
@@ -255,10 +257,12 @@ def test_iter_by_timepoints_full(self):
         self.assertTrue(isgenerator(res))
         for iii, image in enumerate(res):
             # Check lazy-loading
+            self.assertIsNot(image, None)
             self.assertIsNone(image._pixels)
             self.assertEqual(image.path, helpers.TS_FILES_JPG[iii])
             self.assertEqual(image.datetime,
                              helpers.TS_DATES_PARSED[iii])
+            self.assertIsNot(image.pixels, None)
             self.assertEqual(image.pixels.dtype, helpers.TS_JPG_DTYPE)
             self.assertEqual(image.pixels.shape, helpers.TS_JPG_SHAPE)