I feel that conscientious users who test their installations should get a clean test. They cannot be expected to know that this is an 'expected failure' and therefore not really a failure.

Test_tools has the following, which indeed works to skip on installed 3.4.1 but not on built 3.4.1+.

if not sysconfig.is_python_build():
    # XXX some installers do contain the tools, should we detect that
    # and run the tests in that case too?
    raise unittest.SkipTest('test irrelevant for an installed Python')

How about we decorate the two failing tests
   line 156, in test_optional_extension # or
   line 316, in test_get_outputs
with
@unittest.skipUnless(sysconfig.is_python_build(),
'test irrelevant for an installed Python')  # or modify message
?