There is no tests for os.chown except for the invalid input.

Attached the patch to add tests for os.chown. This test has not exercised the keyword `dir_fd` and `follow_symlinks` because `follow_symlinks` (I think) is kinda broken on Windows and I prefer to add unit test for `dir_fd` keyword in different ticket.

Here is the patch for Python 2.7.

Here is the patch that is considerate towards Windows for Python 3.4. I'll fix the patch for Python 2.7 later.

Hi, I left a couple of comments on rietveld.

Here is the patch based on Claudiu's comment and Serhiy's commit (http://hg.python.org/cpython/rev/4b187f5aa960).

Claudiu (Thanks!!!), I can not apply two of your suggestions:
"You could use support.import_module here in order to skip the test if pwd can't be imported."
=> It will skip the entire file if I do that which is bad for Windows.

"You could use assertRaisesRegex."
=> I can not because assertRaisesRegex can not be used with "with" statement.

os.chown is not available on Windows. But maybe pwd can't be built on any Unix system, so not using import_module is okay.

"=> I can not because assertRaisesRegex can not be used with "with" statement."

Not true (see https://docs.python.org/3/library/unittest.html?highlight=assertraisesregex#unittest.TestCase.assertRaisesRegex).

I think you can skip the entire test class if os.chown is not available. Also, maybe you can move the obtaining of groups and users in setUpClass? 
Also, in 

+        with self.assertRaises(PermissionError) as cx:
+            os.chown(support.TESTFN, uid_1, gid)
+            os.chown(support.TESTFN, uid_2, gid)

if the first os.chown will raise the PermissionError, the second one won't be called, maybe that's not what you intended to do.

Claudiu, I have revamped the test and put it in dedicated test class. Thanks!

1. About assertRaisesRegex, sorry, you're right. We can use it with "with" statement. Prior to this, I used it like this:

with self.assertRaisesRegex(PermissionError,
                                    "Operation not permitted"):
    bla
    bla

Then I realized I have to use it like this:

with self.assertRaisesRegex(PermissionError,
                                    "Operation not permitted") as _:
    bla
    bla

2. About this code, it is deliberate:

+        with self.assertRaises(PermissionError) as cx:
+            os.chown(support.TESTFN, uid_1, gid)
+            os.chown(support.TESTFN, uid_2, gid)

Normal user does not have permission to use chown to change the user of the file. Basically, I need to find the other user other than the user of support.TESTFN. By using chown with two users, it will be guaranteed the case will be tried.

There is other way though, iterating all users and check whether the user is not the owner of support.TESTFN or not. If you object it, I can use this way.

Why the need of "as _" in the with statement? I don't understand it. Otherwise, looks good to me.

Okay, I removed "as _". I thought it was not possible.

Looks good to me.

Added a couple review comments on possible further improvements.

The unit test has changed significantly since R. David Murray posted his suggestions, but I've at least moved the test over to the new format as noted in the last comment of the v5 patch.

Here is the patch based on R. David Murray's review. Thanks!

Thanks also for the work of Cormac O'Brien.

Here is the latest patch which executes unittest.main inside __main__ based on R. David Murray's review. Thanks!

New changeset 32c5b9aeee82 by R David Murray in branch 'default':
#20069: Add tests for os.chown.
https://hg.python.org/cpython/rev/32c5b9aeee82

Thanks, Vajrasky.

Tests failed on Solaris:
http://buildbot.python.org/all/builders/AMD64%20Solaris%2011%20%5BSB%5D%203.x/builds/3895/steps/test/logs/stdio

======================================================================
FAIL: test_chown_without_permission (test.test_os.ChownFileTests)
----------------------------------------------------------------------
PermissionError: [Errno 1] Not owner: '@test_18916_tmp'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/cpython/buildslave/cc-32/3.x.snakebite-solaris11-amd64/build/Lib/test/test_os.py", line 1080, in test_chown_without_permission
    os.chown(support.TESTFN, uid_2, gid)
AssertionError: "Operation not permitted" does not match "[Errno 1] Not owner: '@test_18916_tmp'"

----------------------------------------------------------------------

New changeset 4cea99f51bfe by Serhiy Storchaka in branch 'default':
Issue #20069: Fixed test_os on Solaris: error message is platform depended.
https://hg.python.org/cpython/rev/4cea99f51bfe