Added bst validate challenge.

graphs_trees/bst_validate/test_bst_validate.py

@@ -0,0 +1,33 @@
+from nose.tools import assert_equal
+
+
+class TestBstValidate(object):
+
+    def test_bst_validate(self):
+        node = Node(5)
+        insert(node, 8)
+        insert(node, 5)
+        insert(node, 6)
+        insert(node, 4)
+        insert(node, 7)
+        assert_equal(validate_bst(node), True)
+
+        root = Node(5)
+        left = Node(5)
+        right = Node(8)
+        invalid = Node(20)
+        root.left = left
+        root.right = right
+        root.left.right = invalid
+        assert_equal(validate_bst(root), False)
+
+        print('Success: test_bst_validate')
+
+
+def main():
+    test = TestBstValidate()
+    test.test_bst_validate()
+
+
+if __name__ == '__main__':
+    main()