Filed by: ncsoregi [at] mozilla.com
Parsed log: https://treeherder.mozilla.org/logviewer.html#?job_id=262539417&repo=mozilla-inbound
Full log: https://queue.taskcluster.net/v1/task/S__Y__cYQ0WRE1qE5fgI3g/runs/0/artifacts/public/logs/live_backing.log

[task 2019-08-20T20:07:24.671Z] 20:07:24 INFO - TEST-PASS | /webdriver/tests/minimize_window/minimize.py | test_minimize
[task 2019-08-20T20:07:24.671Z] 20:07:24 INFO - TEST-UNEXPECTED-FAIL | /webdriver/tests/minimize_window/minimize.py | test_payload - assert not True
[task 2019-08-20T20:07:24.671Z] 20:07:24 INFO - session = <Session 287ef46f-2f4f-4842-a0b7-4767f7eaee8c>
[task 2019-08-20T20:07:24.671Z] 20:07:24 INFO -
[task 2019-08-20T20:07:24.671Z] 20:07:24 INFO - def test_payload(session):
[task 2019-08-20T20:07:24.671Z] 20:07:24 INFO - > assert not document_hidden(session)
[task 2019-08-20T20:07:24.671Z] 20:07:24 INFO - E assert not True
[task 2019-08-20T20:07:24.671Z] 20:07:24 INFO - E + where True = document_hidden(<Session 287ef46f-2f4f-4842-a0b7-4767f7eaee8c>)
[task 2019-08-20T20:07:24.671Z] 20:07:24 INFO -
[task 2019-08-20T20:07:24.671Z] 20:07:24 INFO - session = <Session 287ef46f-2f4f-4842-a0b7-4767f7eaee8c>
[task 2019-08-20T20:07:24.672Z] 20:07:24 INFO -
[task 2019-08-20T20:07:24.672Z] 20:07:24 INFO - tests/web-platform/tests/webdriver/tests/minimize_window/minimize.py:36: AssertionError
[task 2019-08-20T20:07:24.672Z] 20:07:24 INFO -
[task 2019-08-20T20:07:24.672Z] 20:07:24 INFO - TEST-UNEXPECTED-FAIL | /webdriver/tests/minimize_window/minimize.py | test_minimize_twice_is_idempotent - assert not True
[task 2019-08-20T20:07:24.672Z] 20:07:24 INFO - session = <Session 287ef46f-2f4f-4842-a0b7-4767f7eaee8c>
[task 2019-08-20T20:07:24.672Z] 20:07:24 INFO -
[task 2019-08-20T20:07:24.672Z] 20:07:24 INFO - def test_minimize_twice_is_idempotent(session):
[task 2019-08-20T20:07:24.673Z] 20:07:24 INFO - > assert not document_hidden(session)
[task 2019-08-20T20:07:24.673Z] 20:07:24 INFO - E assert not True
[task 2019-08-20T20:07:24.673Z] 20:07:24 INFO - E + where True = document_hidden(<Session 287ef46f-2f4f-4842-a0b7-4767f7eaee8c>)
[task 2019-08-20T20:07:24.673Z] 20:07:24 INFO -
[task 2019-08-20T20:07:24.673Z] 20:07:24 INFO - session = <Session 287ef46f-2f4f-4842-a0b7-4767f7eaee8c>
[task 2019-08-20T20:07:24.673Z] 20:07:24 INFO -
[task 2019-08-20T20:07:24.673Z] 20:07:24 INFO - tests/web-platform/tests/webdriver/tests/minimize_window/minimize.py:56: AssertionError
[task 2019-08-20T20:07:24.677Z] 20:07:24 INFO - TEST-OK | /webdriver/tests/minimize_window/minimize.py | took 52963ms

Getting the window from minimized to normal state by using Set Window Rect returned too early:

[task 2019-08-20T20:07:14.434Z] 20:07:14 INFO - PID 2111 | 1566331634418 Marionette DEBUG 0 -> [0,98,"WebDriver:SetWindowRect",{"x":100,"y":100}]
[task 2019-08-20T20:07:19.445Z] 20:07:19 INFO - PID 2111 | 1566331639439 Marionette DEBUG 0 <- [1,98,null,{"x":100,"y":100,"width":800,"height":600}]
[task 2019-08-20T20:07:19.445Z] 20:07:19 INFO - PID 2111 | 1566331639440 webdriver::server DEBUG <- 200 OK {"value":{"x":100,"y":100,"width":800,"height":600}}
[task 2019-08-20T20:07:19.451Z] 20:07:19 INFO - PID 2111 | 1566331639441 webdriver::server DEBUG -> POST /session/287ef46f-2f4f-4842-a0b7-4767f7eaee8c/execute/sync {"args": [], "script": "return document.hidden"}
[task 2019-08-20T20:07:19.451Z] 20:07:19 INFO - PID 2111 | 1566331639442 Marionette DEBUG 0 -> [0,99,"WebDriver:ExecuteScript",{"args":[],"script":"return document.hidden"}]
[task 2019-08-20T20:07:19.451Z] 20:07:19 INFO - PID 2111 | 1566331639444 Marionette DEBUG 0 <- [1,99,null,{"value":true}]

It would have been good to see window events in the trace log, but that needs bug 1510940.

https://wiki.mozilla.org/Bug_Triage#Intermittent_Test_Failure_Cleanup