Added a validation test.

src/rules/fractions.py

@@ -235,7 +235,6 @@ def match_divide_fractions(node):
     a / b / c        ->  a / (bc)
     a / (b / c)      ->  ac / b
     """
-    # TODO: IMPLICIT: a / b / (c / d)  ->*  ad / bd  ->  validation test!
     assert node.is_op(OP_DIV)
 
     nom, denom = node

tests/test_validation.py

@@ -12,6 +12,7 @@ class TestValidation(TestCase):
 
     def test_intermediate_success(self):
         self.assertTrue(validate('3a+a+b+2b', '4a+3b'))
+        self.assertTrue(validate('a/b/(c/d)', 'ad/(bc)'))
 
     def test_intermediate_failure(self):
         self.assertFalse(validate('3a+a+b+2b', '4a+4b'))