Since yesterday, if I try to run ./mach test comm/calendar/test/browser/browser_taskUndoRedo.js locally, I get multiple errors all starting with:
FAIL uncaught exception - TypeError: can't access property "every", items is undefined at canEditSelectedItems@chrome://calendar/content/calendar-command-controller.js:851:3

This is one of the many full stack of the failure:

FAIL uncaught exception - TypeError: can't access property "every", items is undefined at canEditSelectedItems@chrome://calendar/content/calendar-command-controller.js:851:3
isCommandEnabled@chrome://calendar/content/calendar-command-controller.js:127:38
goUpdateCommand@chrome://global/content/globalOverlay.js:111:28
updateCommands@chrome://calendar/content/calendar-command-controller.js:107:19
onSelectionChanged@chrome://calendar/content/calendar-command-controller.js:521:24
connectedCallback/<@chrome://calendar/content/calendar-task-tree.js:227:30
modifyItems@chrome://calendar/content/calendar-task-tree-view.js:158:32
addItems@chrome://calendar/content/calendar-task-tree-view.js:68:10
onAddItem@chrome://calendar/content/calendar-task-tree.js:43:29
notify@resource:///modules/calendar/utils/calDataUtils.jsm:39:23
notify@resource:///modules/calendar/utils/calDataUtils.jsm:66:18
onAddItem@resource:///modules/CalCompositeCalendar.jsm:37:34
notify@resource:///modules/calendar/utils/calDataUtils.jsm:39:23
notify@resource:///modules/calendar/utils/calDataUtils.jsm:66:18
adoptItem@resource:///modules/CalMemoryCalendar.jsm:178:21
addItem@resource:///modules/CalMemoryCalendar.jsm:122:17
undoTransaction@resource:///modules/CalTransactionManager.jsm:354:25
undoTransaction@resource:///modules/CalTransactionManager.jsm:231:17
undo@resource:///modules/CalTransactionManager.jsm:119:16
undo@chrome://calendar/content/calendar-item-editing.js:709:24
doCommand@chrome://calendar/content/calendar-command-controller.js:754:9
doCommand@chrome://calendar/content/calendar-tabs.js:139:58
doCommand@chrome://messenger/content/tabmail.js:573:27
goDoCommand@chrome://global/content/globalOverlay.js:128:18
oncommand@chrome://messenger/content/messenger.xhtml:1:12
testDeleteUndoRedoTask@chrome://mochitests/content/browser/comm/calendar/test/browser/browser_taskUndoRedo.js:195:8

I broke it. There's a different (additional) failure when running the whole directory that I'm pretty sure I didn't cause, but I can fix it too.

If this is the only test running then the current view hasn't been initialised, and getSelectedItems will return undefined instead of an array.
Also stops the task tree from setting the view to its existing value, which causes some weirdness to happen.

Pushed by geoff@darktrojan.net:
https://hg.mozilla.org/comm-central/rev/1f758c305c3c
Fix browser_taskUndoRedo.js when run by itself. r=aleca