>     self.assertEqual(self.nroot(x**12, 12), float(x))
> AssertionError: 1.1866666666666665 != 1.1866666666666668

That looks like a case where the test should simply be weakened to an `assertAlmostEqual` with a suitable tolerance; there's no strong reason to expect that `nroot` will give a faithfully rounded result in this case or any other.