Index: Lib/test/test_format.py
===================================================================
--- Lib/test/test_format.py	(revision 76872)
+++ Lib/test/test_format.py	(working copy)
@@ -264,6 +264,30 @@
             else:
                 raise TestFailed('"%*d"%(maxsize, -127) should fail')
 
+
+def with_tolerant_stdout(f):
+    """Decorator to silence UnicodeEncodeError on standard output.
+
+    Example: when standard output is connected to a pipe.
+    """
+    import codecs
+    stdout_encoding = codecs.lookup(sys.stdout.encoding).name
+    if stdout_encoding == 'utf-8':
+        return f
+    def wrapper():
+        stdout_write = sys.stdout.write
+        def safe_write(data):
+            safe_data = data.encode(stdout_encoding, 'backslashreplace').decode(stdout_encoding)
+            return stdout_write(safe_data)
+        sys.stdout.write = safe_write
+        try:
+            f()
+        finally:
+            sys.stdout.write = stdout_write
+    return wrapper
+
+
+@with_tolerant_stdout
 def test_main():
     support.run_unittest(FormatTest)