diff --git a/Lib/test/test_datetime.py b/Lib/test/test_datetime.py
index 7c08f9e..8ac7160 100644
--- a/Lib/test/test_datetime.py
+++ b/Lib/test/test_datetime.py
@@ -851,29 +851,29 @@
 
     def test_format(self):
         dt = self.theclass(2007, 9, 10)
-        self.assertEqual(format(dt, ''), str(dt))
+        self.assertEqual(dt.__format__(''), str(dt))
 
         # check that a derived class's __str__() gets called
         class A(self.theclass):
             def __str__(self):
                 return 'A'
         a = A(2007, 9, 10)
-        self.assertEqual(format(a, ''), 'A')
+        self.assertEqual(a.__format__(''), 'A')
 
         # check that a derived class's strftime gets called
         class B(self.theclass):
             def strftime(self, format_spec):
                 return 'B'
         b = B(2007, 9, 10)
-        self.assertEqual(format(b, ''), str(dt))
+        self.assertEqual(b.__format__(''), str(dt))
 
         for fmt in ["m:%m d:%d y:%y",
                     "m:%m d:%d y:%y H:%H M:%M S:%S",
                     "%z %Z",
                     ]:
-            self.assertEqual(format(dt, fmt), dt.strftime(fmt))
-            self.assertEqual(format(a, fmt), dt.strftime(fmt))
-            self.assertEqual(format(b, fmt), 'B')
+            self.assertEqual(dt.__format__(fmt), dt.strftime(fmt))
+            self.assertEqual(a.__format__(fmt), dt.strftime(fmt))
+            self.assertEqual(b.__format__(fmt), 'B')
 
     def test_resolution_info(self):
         self.assert_(isinstance(self.theclass.min, self.theclass))
@@ -1178,31 +1178,29 @@
 
     def test_format(self):
         dt = self.theclass(2007, 9, 10, 4, 5, 1, 123)
-        self.assertEqual(format(dt, ''), str(dt))
+        self.assertEqual(dt.__format__(''), str(dt))
 
         # check that a derived class's __str__() gets called
         class A(self.theclass):
             def __str__(self):
                 return 'A'
         a = A(2007, 9, 10, 4, 5, 1, 123)
-        self.assertEqual(format(a, ''), 'A')
+        self.assertEqual(a.__format__(''), 'A')
 
         # check that a derived class's strftime gets called
         class B(self.theclass):
             def strftime(self, format_spec):
                 return 'B'
         b = B(2007, 9, 10, 4, 5, 1, 123)
-        self.assertEqual(format(b, ''), str(dt))
+        self.assertEqual(b.__format__(''), str(dt))
 
         for fmt in ["m:%m d:%d y:%y",
                     "m:%m d:%d y:%y H:%H M:%M S:%S",
                     "%z %Z",
                     ]:
-            self.assertEqual(format(dt, fmt), dt.strftime(fmt))
-            self.assertEqual(format(a, fmt), dt.strftime(fmt))
-            self.assertEqual(format(b, fmt), 'B')
-
-
+            self.assertEqual(dt.__format__(fmt), dt.strftime(fmt))
+            self.assertEqual(a.__format__(fmt), dt.strftime(fmt))
+            self.assertEqual(b.__format__(fmt), 'B')
 
     def test_more_ctime(self):
         # Test fields that TestDate doesn't touch.
@@ -1837,27 +1835,27 @@
 
     def test_format(self):
         t = self.theclass(1, 2, 3, 4)
-        self.assertEqual(format(t, ''), str(t))
+        self.assertEqual(t.__format__(''), str(t))
 
         # check that a derived class's __str__() gets called
         class A(self.theclass):
             def __str__(self):
                 return 'A'
         a = A(1, 2, 3, 4)
-        self.assertEqual(format(a, ''), 'A')
+        self.assertEqual(a.__format__(''), 'A')
 
         # check that a derived class's strftime gets called
         class B(self.theclass):
             def strftime(self, format_spec):
                 return 'B'
         b = B(1, 2, 3, 4)
-        self.assertEqual(format(b, ''), str(t))
+        self.assertEqual(b.__format__(''), str(t))
 
         for fmt in ['%H %M %S',
                     ]:
-            self.assertEqual(format(t, fmt), t.strftime(fmt))
-            self.assertEqual(format(a, fmt), t.strftime(fmt))
-            self.assertEqual(format(b, fmt), 'B')
+            self.assertEqual(t.__format__(fmt), t.strftime(fmt))
+            self.assertEqual(a.__format__(fmt), t.strftime(fmt))
+            self.assertEqual(b.__format__(fmt), 'B')
 
     def test_str(self):
         self.assertEqual(str(self.theclass(1, 2, 3, 4)), "01:02:03.000004")