Store edge IDs as integer in the dependency graph.

add_dependency would store them as strings. On the next invocation
of add_dependency, find_new_id wouldn't find the previously stored
value since it looks for integers. Therefore it returns the same
ID, resulting in duplicate edge IDs.

TodoList.py

@@ -196,7 +196,7 @@ class TodoList(object):
                 from_todo.set_tag('id', dep_id)
 
             to_todo.add_tag('p', dep_id)
-            self._depgraph.add_edge(p_number1, p_number2, int(dep_id))
+            self._depgraph.add_edge(p_number1, p_number2, dep_id)
             self._update_parent_cache()
 
     def remove_dependency(self, p_number1, p_number2):

test/TodoListTest.py

@@ -167,12 +167,24 @@ class TodoListDependencyTester(unittest.TestCase):
         self.assertEqual(self.todolist.children(2), [])
         self.assertEqual(self.todolist.parents(1), [])
 
-    def test_add_dep(self):
+    def test_add_dep1(self):
         self.todolist.add_dependency(5, 4)
 
         self.assertTrue(self.todolist.todo(5).has_tag('id', '3'))
         self.assertTrue(self.todolist.todo(4).has_tag('p', '3'))
 
+    def test_add_dep2(self):
+        """
+        Make sure that previous add_dependency invocation stored the
+        edge_id properly.
+        """
+
+        self.todolist.add_dependency(5, 4)
+        self.todolist.add_dependency(4, 1)
+
+        self.assertTrue(self.todolist.todo(4).has_tag('id', '4'))
+        self.assertTrue(self.todolist.todo(1).has_tag('p', '4'))
+
     def test_remove_dep1(self):
         self.todolist.remove_dependency(3, 4)