Is an accurate socionics test impossible?
IM elements are so abstract that I'm not sure people can reliably determine them for themselves. Not individually. However I think by contrasting lists of definite processes together we may be able to make a better socionics test.
But, observation of the political dimension for such a test is essential, because the functions themselves are composited of political opposites. (change vs continuity) Such a test would also need to be stood by by persons of strong will, because radicals would be determined to declare the existence of the functional orientations they despise null and void.