fix assertRaises, that was actually not testing anything

The function did in fact return None, but the assertRaises was wrongly
written, so it did not test that the function raises anything.

experiments/tests/test_significance.py

@@ -39,8 +39,8 @@ def test_equal(self):
         self.assertChiSquareCorrect(((100, 100, 100), (200, 200, 200), (300, 300, 300)), 0, 1)
 
     def test_error(self):
-        self.assertRaises(TypeError, chi_square_p_value((1,)))
-        self.assertRaises(TypeError, chi_square_p_value(((1,2,3))))
+        self.assertEqual(chi_square_p_value((1,)), None)
+        self.assertEqual(chi_square_p_value(((0,2,3))), None)
 
     def test_is_none(self):
         self.assertEqual(chi_square_p_value(((1, 1), (1, -1))), (None, None), "Negative numbers should not be allowed")