x/sys/unix: TestSCMCredentials failing on Linux with Go 1.8 and Go 1.9

[bradfitz]

Go supports the past two releases. https://build.golang.org/ shows that x/sys is broken on Linux for Go 1.8 and Go 1.9 due to:

?   	golang.org/x/sys/plan9	[no test files]
--- FAIL: TestSCMCredentials (0.00s)
	creds_test.go:112: ReadMsgUnix n = 1, want 0
FAIL
FAIL	golang.org/x/sys/unix	0.223s
?   	golang.org/x/sys/windows	[no test files]
?   	golang.org/x/sys/windows/registry	[no test files]

tests failed: exit status 1

@lucab, can you fix? Looks like it was from https://go-review.googlesource.com/c/sys/+/60190 perhaps?

[lucab]

Oh yes, I caused the test regression with that commit, sorry.

However I think the test in there is inherently broken and I'm not sure how to proceed. The reason is that TestSCMCredentials is actually testing behavior which belongs to net.UnixConn.WriteMsgUnix(). As such, test result depends on whatever the stdlib is doing, and in particular whether https://go.googlesource.com/go/+/93da0b6e66f24c4c307e0df37ceb102a33306174 is present.

I'd like to get your input on how you would like this test to be amended. I can suggest two options:

• drop this test completely, as it is an exact copy of the one in unix.
• relax the length checking, as that behavior belongs to unix. This is probably better as it would keep coverage fo x/sys/unix.Parse*(), but I'm unsure how useful it is.

[gopherbot]

Change https://golang.org/cl/80275 mentions this issue: unix: skip TestSCMCredentials SOCK_DGRAM test before 1.10

[ianlancetaylor]

I think we should just skip the test on earlier revisions. Sent https://golang.org/cl/80275.