Added new Leiden practice addignments to unit tests.

tests/test_leiden_oefenopgave_v12.py

@@ -0,0 +1,21 @@
+from tests.rulestestcase import RulesTestCase as TestCase, rewrite
+
+
+class TestLeidenOefenopgaveV12(TestCase):
+    def test_1_e(self):
+        for chain in [['-2(6x - 4) ^ 2 * x',
+                       '-2(6x - 4)(6x - 4)x',
+                       '(-2 * 6x - 2 * -4)(6x - 4)x',
+                       '(-12x - 2 * -4)(6x - 4)x',
+                       '(-12x - -8)(6x - 4)x',
+                       '(-12x + 8)(6x - 4)x',
+                       '(-12x * 6x - 12x * -4 + 8 * 6x + 8 * -4)x',
+                       '(-72xx - 12x * -4 + 8 * 6x + 8 * -4)x',
+                       '(-72 * x ^ (1 + 1) - 12x * -4 + 8 * 6x + 8 * -4)x',
+                       '(-72 * x ^ 2 - 12x * -4 + 8 * 6x + 8 * -4)x',
+                       '(-72 * x ^ 2 - -48x + 8 * 6x + 8 * -4)x',
+                       '(-72 * x ^ 2 - -48x + 48x + 8 * -4)x',
+                       '',
+                       '']
+            ]:
+            self.assertRewrite(chain)