I don't follow what you did when you wrote:

Ensure that "groups" includes a numeric group, e.g.:

What is the following output?

Sent https://go-review.googlesource.com/20642 for the error formatting at least.

CL https://golang.org/cl/20642 mentions this issue.

"groups" is a command on OSX. The output that follows is a list of the groups I am in, with some of the employer-specific ones elided with "...". For whatever reason, I seem to be in group 5000 on my laptop. The test either needs to run in a more controlled environment, or be more tolerant of apparently peculiar environments.

What did you do to add yourself to such a group, though?

there seems to be more needed than just a group with a numeric name:
sudo dseditgroup -o create -r "5000" 5000
sudo dseditgroup -o edit -a USERNAMETOADD -t user 5000

whats the output of (e.g. to see the groupid):
sudo dseditgroup -o read 5000
?

For grins:

ls -lg ~
total 18088
drwx------   5 5000      170 Jan 20 11:41 Applications
drwx------+ 23 5000      782 Feb 19 12:45 Desktop
drwx------+ 31 5000     1054 Jan 19 22:57 Documents
drwx------+ 59 5000     2006 Mar 11 15:21 Downloads
...

I have no idea what/why/how, I try not to do a lot of hacking at my laptop's configuration.

"What did you do to add yourself to such a group, though?"
Accepted employment at Google and took the company-issued laptop.

ls -lgd ~
drwxr-xr-x+ 76 5000  2584 Mar 13 14:01 /Users/drchase

My account was apparently born that way.

I am having a similar issue. Go at tip used to pass all tests. Now it fails with the following:

--- FAIL: TestLookupGroup (0.00s)
user_test.go:107: LookupGroupId("2110994482"): group: unknown groupid 2110994482
FAIL
FAIL os/user 0.027s

@dr2chase Odd. I was also testing on a Google-issued darwin laptop. :)

The test may need to be removed. As identified here, it fails in misconfigured environments where a user is not a part of their primary group. Unfortunately, I don't think there's a cross-platform way to make this test hermetic. However, the underlying getgrouplist call is documented to always add the supplied gid to the list, so this surprises me.

@bradfitz Should I go ahead and move all platforms to the /etc/group fallback? Seems more reliable than all the woes that my CL has introduced. Sorry that this has created so much noise.

For both of you, it would be helpful to know the number of supplementary groups your user is a part of -- is it greater than 256?

@zombiezen It returns 116 for me

dscl . list /groups|wc -l
116

For me:

dscl . list /groups|wc -l
     120

@zombiezen, /etc/group fallback sounds good if you'd like. But only if it's actually a fallback; we should probably still try using C first. I'll leave it up to you as to how to change the tests.