runtest(): When generating output, if the result is a single line with the

name of the test, only write the output file if it already exists (and
    tell the user to consider removing it).  This avoids the generation of
    unnecessary turds.

Lib/test/regrtest.py

@@ -230,7 +230,7 @@ def runtest(test, generate, verbose, quiet, testdir = None):
     outputfile = os.path.join(outputdir, test)
     try:
         if generate:
-            cfp = open(outputfile, "w")
+            cfp = StringIO.StringIO()
         elif verbose:
             cfp = sys.stdout
         else:
@@ -273,6 +273,24 @@ def runtest(test, generate, verbose, quiet, testdir = None):
             traceback.print_exc(file=sys.stdout)
         return 0
     else:
+        if generate:
+            output = cfp.getvalue()
+            if output == test + "\n":
+                if os.path.exists(outputfile):
+                    # Write it since it already exists (and the contents
+                    # may have changed), but let the user know it isn't
+                    # needed:
+                    fp = open(outputfile, "w")
+                    fp.write(output)
+                    fp.close()
+                    print "output file", outputfile, \
+                          "is no longer needed; consider removing it"
+                # else:
+                #     We don't need it, so don't create it.
+            else:
+                fp = open(outputfile, "w")
+                fp.write(output)
+                fp.close()
         return 1
 
 def findtestdir():