Index: Lib/test/test_support.py
===================================================================
--- Lib/test/test_support.py	(revision 77755)
+++ Lib/test/test_support.py	(working copy)
@@ -438,15 +438,22 @@
     testcase.assertRaises(SyntaxError, compile, statement,
                           '<test string>', 'exec')
 
-def open_urlresource(url):
+def open_urlresource(url, check=lambda f: True):
     import urlparse, urllib2
 
-    requires('urlfetch')
     filename = urlparse.urlparse(url)[2].split('/')[-1] # '/': it's URL!
 
     fn = os.path.join(os.path.dirname(__file__), "data", filename)
     if os.path.exists(fn):
-        return open(fn)
+        f = open(fn)
+        if check(f):
+            f.seek(0)
+            return f
+        f.close()
+        unlink(fn)
+
+    # Verify the requirement if we *really* need to download the file
+    requires('urlfetch')
 
     print >> get_original_stdout(), '\tfetching %s ...' % url
     f = urllib2.urlopen(url, timeout=15)
@@ -458,7 +465,12 @@
                 s = f.read()
     finally:
         f.close()
-    return open(fn)
+    f = open(fn)
+    if not check(f):
+        f.close()
+        raise TestFailed('invalid resource "%s"' % fn)
+    f.seek(0)
+    return f
 
 
 class WarningsRecorder(object):