def test__namesOfDoubleAttributes(self):
"""check Attributes._namesOfDoubleAttributes()
"""
a = Attributes()
self.assertEqual(0, len(a._namesOfDoubleAttributes()))
pq = PairQuantity()
self.assertNotEqual(0, len(pq._namesOfDoubleAttributes()))
self.assertFalse('bar' in pq._namesOfDoubleAttributes())
pq._registerDoubleAttribute('bar')
self.assertTrue('bar' in pq._namesOfDoubleAttributes())
return
