1399018 - Intermittent test_expected.py TestExpected.test_element_displayed_when_stale_element | UnknownException: TypeError: el is null

Status: RESOLVED FIXED

(Testing :: Marionette Client and Harness, defect, P5)

Description

[Treeherder Bug Filer]

Filed by: philringnalda [at] gmail.com

https://treeherder.mozilla.org/logviewer.html#?job_id=130272220&repo=mozilla-inbound

https://queue.taskcluster.net/v1/task/BsK7LYE8TE2RjEOtjsdBgA/runs/0/artifacts/public/logs/live_backing.log

Comment 1

[Henrik Skupin [:whimboo][⌚️UTC+2]]

Here the failing test:

https://dxr.mozilla.org/mozilla-central/rev/f9a5e9ed62103c84e4cde915f4d08f1ce71be83e/testing/marionette/harness/marionette_harness/tests/unit/test_expected.py#146-151

The JS error stack looks like:

05:52:51     INFO -  	element.isStale@chrome://marionette/content/element.js:636:7
05:52:51     INFO -  	get@chrome://marionette/content/element.js:181:9
05:52:51     INFO -  	isElementDisplayed@chrome://marionette/content/listener.js:1431:12
05:52:51     INFO -  	dispatch/</req<@chrome://marionette/content/listener.js:515:16
05:52:51     INFO -  	async*dispatch/<@chrome://marionette/content/listener.js:513:16

It means that we have to caught the `TypeError` and let `isStale` return false, but that doesn't happen:
https://dxr.mozilla.org/mozilla-central/rev/f9a5e9ed62103c84e4cde915f4d08f1ce71be83e/testing/marionette/element.js#635-643

It's a regression from the changes on bug 1394881. Andreas, can you please have a look?

Comment 2

[Andreas Tolfsen ❲:ato❳]

Unable to reproduce this, but the only thing I can think of from the
element.Store is that el.get(), is that it fails when unpacking the
weak reference of the element:

>   get(uuid) {
>     let el = this.els[uuid];
>     if (!el) {
>       throw new NoSuchElementError("Element reference not seen before: " + uuid);
>     }
> 
>     try {
>       el = el.get();
>     } catch (e) {
>       el = null;
>       delete this.els[uuid];
>     }
> 
>     if (element.isStale(el)) {
>       throw new StaleElementReferenceError(
>           pprint`The element reference of ${el} stale; ` +
>               "either the element is no longer attached to the DOM " +
>               "or the document has been refreshed");
>     }
> 
>     return el;
>   }

Arguably we should error when el.get() throws and the weak reference
is deleted from the cache.

Comment 3

[Andreas Tolfsen ❲:ato❳]

(In reply to Andreas Tolfsen ‹:ato› from comment #2)

> Arguably we should error when el.get() throws and the weak
> reference is deleted from the cache.

Filed https://bugzilla.mozilla.org/show_bug.cgi?id=1399076 to take
care of this.

Comment 4

[Jim Mathies [:jimm]]

based on priority

Comment 5

[David Burns :automatedtester]

appears to have been fixed by bug 1399076

Comment 6

[BMO Automation]

Moving bug to Testing::Marionette Client and Harness component per bug 1815831.