[+crouleau]:  Possibly the same as  issue 822256 , which you marked as fixed?

I was just being the Chromium Build sheriff. I don't have any information other than what is in the bug. It was failing and then I reverted a change and then it stopped failing so I marked it fixed.

Sorry I can't be more helpful.

Looks like this hasn't been fixed; three more failures in the last three days:
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac10.10%20Tests/31754
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac10.10%20Tests/31710
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac10.10%20Tests/31662

[+iannucci]:  Maybe related to the vpython switch /  issue 822256  and issue 804174?  Test seems to be hanging while starting the python test server.

 Issue 839422  has been merged into this issue.

I don't know the significance, but many of the test logs do have vpython errors:

https://logs.chromium.org/v/?s=chromium%2Fbuildbucket%2Fcr-buildbucket.appspot.com%2F8947542763357872384%2F%2B%2Fsteps%2Fnet_unittests_on_Mac-10.10%2F0%2Fstdout

[ RUN      ] URLRequestTestFTP.RawBodyBytes
[E2018-05-03T07:11:30.376412-07:00 4667 0 annotate.go:242] goroutine 1:
[E2018-05-03T07:11:30.376501-07:00 4667 0 annotate.go:242] #0 go.chromium.org/luci/vpython/venv/venv.go:475 - venv.(*Env).createLocked()
[E2018-05-03T07:11:30.376544-07:00 4667 0 annotate.go:242]   reason: failed to remove existing root
[E2018-05-03T07:11:30.376613-07:00 4667 0 annotate.go:242] 
[E2018-05-03T07:11:30.376643-07:00 4667 0 annotate.go:242] #1 go.chromium.org/luci/vpython/venv/venv.go:272 - venv.(*Env).ensure.func1()
[E2018-05-03T07:11:30.376688-07:00 4667 0 annotate.go:242]   reason: failed to create new VirtualEnv
[E2018-05-03T07:11:30.376714-07:00 4667 0 annotate.go:242] 
[E2018-05-03T07:11:30.376739-07:00 4667 0 annotate.go:242] #2 go.chromium.org/luci/vpython/venv/venv.go:955 - venv.mustReleaseLock()
[E2018-05-03T07:11:30.377148-07:00 4667 0 annotate.go:242] #3 go.chromium.org/luci/vpython/venv/venv.go:258 - venv.(*Env).ensure()
[E2018-05-03T07:11:30.377178-07:00 4667 0 annotate.go:242] #4 go.chromium.org/luci/vpython/venv/venv.go:328 - venv.(*Env).withImpl()
[E2018-05-03T07:11:30.377206-07:00 4667 0 annotate.go:242] #5 go.chromium.org/luci/vpython/venv/venv.go:168 - venv.With()
[E2018-05-03T07:11:30.377269-07:00 4667 0 annotate.go:242] #6 go.chromium.org/luci/vpython/run.go:63 - vpython.Run()
[E2018-05-03T07:11:30.377295-07:00 4667 0 annotate.go:242] #7 go.chromium.org/luci/vpython/application/application.go:318 - application.(*application).mainImpl()
[E2018-05-03T07:11:30.377342-07:00 4667 0 annotate.go:242] #8 go.chromium.org/luci/vpython/application/application.go:402 - application.(*Config).Main.func1()
[E2018-05-03T07:11:30.377372-07:00 4667 0 annotate.go:242] #9 go.chromium.org/luci/vpython/application/support.go:47 - application.run()
[E2018-05-03T07:11:30.377399-07:00 4667 0 annotate.go:242] #10 go.chromium.org/luci/vpython/application/application.go:401 - application.(*Config).Main()
[E2018-05-03T07:11:30.377434-07:00 4667 0 annotate.go:242] #11 vpython/main.go:92 - main.mainImpl()
[E2018-05-03T07:11:30.377460-07:00 4667 0 annotate.go:242] #12 vpython/main.go:98 - main.main()
[E2018-05-03T07:11:30.377485-07:00 4667 0 annotate.go:242] #13 runtime/proc.go:195 - runtime.main()
[E2018-05-03T07:11:30.377511-07:00 4667 0 annotate.go:242] #14 runtime/asm_amd64.s:2337 - runtime.goexit()
[4189:779:0503/071130.379904:43345824371351:ERROR:local_test_server_posix.cc(169)] Could not read server_data_len
../../net/url_request/url_request_unittest.cc:12391: Failure
Value of: ftp_test_server_.Start()
  Actual: false
Expected: true
Stack trace:
0   net_unittests                       0x000000010497236b testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop(int) + 91
1   net_unittests                       0x0000000104971d29 testing::internal::AssertHelper::operator=(testing::Message const&) const + 89
2   net_unittests                       0x000000010464ee0f net::URLRequestTestFTP_RawBodyBytes_Test::TestBody() + 559
[  FAILED  ] URLRequestTestFTP.RawBodyBytes (834 ms)

[ RUN      ] WebSocketEndToEndTest.HstsHttpsToWebSocket
[E2018-05-03T07:11:30.644456-07:00 4673 0 config.go:310] Failed to get runtime information:
         {"error":"exit status 1"}
[E2018-05-03T07:11:30.644893-07:00 4673 0 annotate.go:242] original error: exit status 1
[E2018-05-03T07:11:30.644930-07:00 4673 0 annotate.go:242] 
[E2018-05-03T07:11:30.644970-07:00 4673 0 annotate.go:242] goroutine 1:
[E2018-05-03T07:11:30.644999-07:00 4673 0 annotate.go:242] #0 go.chromium.org/luci/vpython/venv/config.go:311 - venv.fillRuntime()
[E2018-05-03T07:11:30.645037-07:00 4673 0 annotate.go:242]   reason: failed to get runtime information
[E2018-05-03T07:11:30.645065-07:00 4673 0 annotate.go:242] 
[E2018-05-03T07:11:30.645084-07:00 4673 0 annotate.go:242] #1 go.chromium.org/luci/vpython/venv/config.go:194 - venv.(*Config).makeEnv()
[E2018-05-03T07:11:30.645102-07:00 4673 0 annotate.go:242] #2 go.chromium.org/luci/vpython/venv/venv.go:163 - venv.With()
[E2018-05-03T07:11:30.645119-07:00 4673 0 annotate.go:242] #3 go.chromium.org/luci/vpython/run.go:63 - vpython.Run()
[E2018-05-03T07:11:30.645136-07:00 4673 0 annotate.go:242] #4 go.chromium.org/luci/vpython/application/application.go:318 - application.(*application).mainImpl()
[E2018-05-03T07:11:30.645178-07:00 4673 0 annotate.go:242] #5 go.chromium.org/luci/vpython/application/application.go:402 - application.(*Config).Main.func1()
[E2018-05-03T07:11:30.645207-07:00 4673 0 annotate.go:242] #6 go.chromium.org/luci/vpython/application/support.go:47 - application.run()
[E2018-05-03T07:11:30.645231-07:00 4673 0 annotate.go:242] #7 go.chromium.org/luci/vpython/application/application.go:401 - application.(*Config).Main()
[E2018-05-03T07:11:30.645272-07:00 4673 0 annotate.go:242] #8 vpython/main.go:92 - main.mainImpl()
[E2018-05-03T07:11:30.645291-07:00 4673 0 annotate.go:242] #9 vpython/main.go:98 - main.main()
[E2018-05-03T07:11:30.645325-07:00 4673 0 annotate.go:242] #10 runtime/proc.go:195 - runtime.main()
[E2018-05-03T07:11:30.645354-07:00 4673 0 annotate.go:242] #11 runtime/asm_amd64.s:2337 - runtime.goexit()
[4399:779:0503/071130.647392:43346091853374:ERROR:local_test_server_posix.cc(169)] Could not read server_data_len
../../net/websockets/websocket_end_to_end_test.cc:396: Failure
Value of: wss_server.Start()
  Actual: false
Expected: true
Stack trace:
0   net_unittests                       0x0000000102fa336b testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop(int) + 91
1   net_unittests                       0x0000000102fa2d29 testing::internal::AssertHelper::operator=(testing::Message const&) const + 89
2   net_unittests                       0x0000000102df9477 net::(anonymous namespace)::WebSocketEndToEndTest_HstsHttpsToWebSocket_Test::TestBody() + 967
[  FAILED  ] WebSocketEndToEndTest.HstsHttpsToWebSocket (379 ms)

etc..

These are the most interesting errors:

[E2018-05-03T07:11:30.376412-07:00 4667 0 annotate.go:242] goroutine 1:
[E2018-05-03T07:11:30.376501-07:00 4667 0 annotate.go:242] #0 go.chromium.org/luci/vpython/venv/venv.go:475 - venv.(*Env).createLocked()
[E2018-05-03T07:11:30.376544-07:00 4667 0 annotate.go:242]   reason: failed to remove existing root
[E2018-05-03T07:11:30.376613-07:00 4667 0 annotate.go:242] 
[E2018-05-03T07:11:30.376643-07:00 4667 0 annotate.go:242] #1 go.chromium.org/luci/vpython/venv/venv.go:272 - venv.(*Env).ensure.func1()
[E2018-05-03T07:11:30.376688-07:00 4667 0 annotate.go:242]   reason: failed to create new VirtualEnv
[E2018-05-03T07:11:30.376714-07:00 4667 0 annotate.go:242] 

Effectively, this means that the Python code will have no environment to run in, and will likely fail to run even the basic system stuff. This might happen if the directory it's trying to write doesn't have write permissions. Since this is invoked from C++, and I'm not familiar with how tests are structured, but I wonder if they have some sort of lockdown mechanism for the file system making it read-only.

Hm, this is very similar to issue 846378, where the same error happens during initial bot_update is ran.

I think same root cause as in issue 846378, will be fixed there.