bpo-31904: Disable os.popen and popen test cases on VxWorks (GH-21687)

diff --git a/Lib/test/test_select.py b/Lib/test/test_select.py
index 4ddd5fb..f63564e 100644
--- a/Lib/test/test_select.py
+++ b/Lib/test/test_select.py
@@ -46,6 +46,7 @@ def test_returned_list_identity(self):
         self.assertIsNot(r, x)
         self.assertIsNot(w, x)
 
+    @unittest.skipUnless(hasattr(os, 'popen'), "need os.popen()")
     def test_select(self):
         code = textwrap.dedent('''
             import time