subp: support combine_capture argument.

This adds 'combine_capture' argument as was present in curtin's
subp.  It is useful to get interleaved output of a command.  I noticed
a need for it when looking at user_data_rhevm in DataSourceAltCloud.
That will run a subcommand, logging its stdout but swallowing its stderr.

Another thing to change to use this would be in udevadm_settle which
currently just returns the subp() call.

Also, add the docstring copied from curtin's subp.

1 files changed, 8 insertions, 0 deletions

diff --git a/tests/unittests/test_util.py b/tests/unittests/test_util.py
index d774f3dc..2db8e3fa 100644
--- a/tests/unittests/test_util.py
+++ b/tests/unittests/test_util.py
@@ -829,6 +829,14 @@ class TestSubp(helpers.CiTestCase):
                                r'Missing #! in script\?',
                                util.subp, (noshebang,))
 
+    def test_subp_combined_stderr_stdout(self):
+        """Providing combine_capture as True redirects stderr to stdout."""
+        data = b'hello world'
+        (out, err) = util.subp(self.stdin2err, capture=True,
+                               combine_capture=True, decode=False, data=data)
+        self.assertEqual(b'', err)
+        self.assertEqual(data, out)
+
     def test_returns_none_if_no_capture(self):
         (out, err) = util.subp(self.stdin2out, data=b'', capture=False)
         self.assertIsNone(err)