Issue #20549: Use specific asserts in mailbox, smtplib and poplib tests.
diff --git a/Lib/test/test_poplib.py b/Lib/test/test_poplib.py
index e9b6daf..af48fdd 100644
--- a/Lib/test/test_poplib.py
+++ b/Lib/test/test_poplib.py
@@ -308,7 +308,7 @@
             serv.close()
 
     def testTimeoutDefault(self):
-        self.assertTrue(socket.getdefaulttimeout() is None)
+        self.assertIsNone(socket.getdefaulttimeout())
         socket.setdefaulttimeout(30)
         try:
             pop = poplib.POP3(HOST, self.port)
@@ -318,13 +318,13 @@
         pop.sock.close()
 
     def testTimeoutNone(self):
-        self.assertTrue(socket.getdefaulttimeout() is None)
+        self.assertIsNone(socket.getdefaulttimeout())
         socket.setdefaulttimeout(30)
         try:
             pop = poplib.POP3(HOST, self.port, timeout=None)
         finally:
             socket.setdefaulttimeout(None)
-        self.assertTrue(pop.sock.gettimeout() is None)
+        self.assertIsNone(pop.sock.gettimeout())
         pop.sock.close()
 
     def testTimeoutValue(self):