#7960: merge with 3.1.

diff --cc Lib/test/support.py
index bd35fded3567d0b176b4134030ab8654b00bc27b,b3b1bbdc2d349526990dfe8ee536dbe4814d5eaf..b1ca9ddebf968ef8ad31ec5198a1368188acc719
--- 1/Lib/test/support.py
--- 2/Lib/test/support.py
+++ b/Lib/test/support.py
@@@ -908,14 -723,14 +902,20 @@@ def captured_output(stream_name)
          setattr(sys, stream_name, orig_stdout)
  
  def captured_stdout():
+     """Capture the output of sys.stdout:
+ 
+        with captured_stdout() as s:
+            print("hello")
+        self.assertEqual(s.getvalue(), "hello")
+     """
      return captured_output("stdout")
  
 +def captured_stderr():
 +    return captured_output("stderr")
 +
 +def captured_stdin():
 +    return captured_output("stdin")
 +
  def gc_collect():
      """Force as many objects as possible to be collected.