Added queue from stacks challenge.

stacks_queues/queue_from_stacks/test_queue_from_stacks.py

@@ -0,0 +1,37 @@
+from nose.tools import assert_equal
+
+
+class TestQueueFromStacks(object):
+    
+    def test_queue_from_stacks(self):
+        print('Test: Dequeue on empty stack')
+        queue = QueueFromStacks()
+        assert_equal(queue.dequeue(), None)
+
+        print('Test: Enqueue on empty stack')
+        print('Test: Enqueue on non-empty stack')
+        print('Test: Multiple enqueue in a row')
+        num_items = 3
+        for i in range (0, num_items):
+            queue.enqueue(i)
+
+        print('Test: Dequeue on non-empty stack')
+        print('Test: Dequeue after an enqueue')
+        assert_equal(queue.dequeue(), 0)
+
+        print('Test: Multiple dequeue in a row')
+        assert_equal(queue.dequeue(), 1)
+        assert_equal(queue.dequeue(), 2)
+
+        print('Test: Enqueue after a dequeue')
+        queue.enqueue(5)
+        assert_equal(queue.dequeue(), 5)
+
+        print('Success: test_queue_from_stacks')
+
+def main():
+    test = TestQueueFromStacks()
+    test.test_queue_from_stacks()
+    
+if __name__ == '__main__':
+    main()