diff -r 2c4448bbed1f Lib/test/test_string.py
--- a/Lib/test/test_string.py	Thu Feb 25 01:35:21 2016 +1100
+++ b/Lib/test/test_string.py	Wed Feb 24 22:33:05 2016 -0500
@@ -1,5 +1,5 @@
 import unittest, string
-
+from string import Template
 
 class ModuleTest(unittest.TestCase):
 
@@ -186,6 +186,18 @@
             fmt._vformat("{i}", args, kwargs, set(), -1)
         self.assertIn("recursion", str(err.exception))
 
+    def test_substitute(self):
+        temp = Template('$abc 456 $xyz')
+        sub = dict(abc='123', xyz='789')
+        self.assertEqual(temp.substitute(sub), '123 456 789')
+        self.assertEqual(temp.safe_substitute(sub), '123 456 789')
+        temp = Template('abc $456 $xyz')
+        with self.assertRaises(ValueError):
+            temp.substitute(sub)
+        temp = Template('$abc 456 $xyz $extra')
+        with self.assertRaises(KeyError):
+            temp.substitute(sub)
+        self.assertEqual(temp.safe_substitute(sub), '123 456 789 $extra')
 
 if __name__ == "__main__":
     unittest.main()