Test currency not implemented, remove dead method.

tests/test_base.py

@@ -0,0 +1,17 @@
+from __future__ import unicode_literals
+
+from decimal import Decimal
+from unittest import TestCase
+
+from num2words.base import Num2Word_Base
+
+
+class Num2WordBaseTest(TestCase):
+    @classmethod
+    def setUpClass(cls):
+        super(Num2WordBaseTest, cls).setUpClass()
+        cls.base = Num2Word_Base()
+
+    def test_to_currency_not_implemented(self):
+        with self.assertRaises(NotImplementedError):
+            self.base.to_currency(Decimal('1.00'), currency='EUR')