Add bst successor challenge.

graphs_trees/bst_successor/test_bst_successor.py

@@ -0,0 +1,36 @@
+from nose.tools import assert_equal
+
+
+class TestBstSuccessor(object):
+
+    def test_bst_successor(self):
+        nodes = {}
+        node = Node(5)
+        nodes[5] = node
+        nodes[3] = insert(node, 3)
+        nodes[8] = insert(node, 8)
+        nodes[2] = insert(node, 2)
+        nodes[4] = insert(node, 4)
+        nodes[6] = insert(node, 6)
+        nodes[12] = insert(node, 12)
+        nodes[1] = insert(node, 1)
+        nodes[7] = insert(node, 7)
+        nodes[10] = insert(node, 10)
+        nodes[15] = insert(node, 15)
+        nodes[9] = insert(node, 9)
+
+        assert_equal(bst_successor(nodes[4]), 5)
+        assert_equal(bst_successor(nodes[5]), 6)
+        assert_equal(bst_successor(nodes[8]), 9)
+        assert_equal(bst_successor(nodes[15]), None)
+
+        print('Success: test_bst_successor')
+
+
+def main():
+    test = TestBstSuccessor()
+    test.test_bst_successor()
+
+
+if __name__ == '__main__':
+    main()