[stable10] Test Helper to read file from server

[individual-it]

backport of #35151

[dpakach]

LGTM 👍

[phil-davis]

https://drone.owncloud.com/owncloud/core/17168/903
Firefox WebDriver\Exception\JavaScriptError: ReferenceError: jQuery is not defined
Build info: version: '3.8.1', revision: '6e95a6684b', time: '2017-12-01T19:05:32.194Z'
so this still happens sometimes.

Restarted drone.

[codecov]

Codecov Report

Merging #35158 into stable10 will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             stable10   #35158   +/-   ##
===========================================
  Coverage       64.47%   64.47%           
  Complexity      20070    20070           
===========================================
  Files            1288     1288           
  Lines           76936    76936           
  Branches         1307     1307           
===========================================
  Hits            49606    49606           
  Misses          26949    26949           
  Partials          381      381

Flag	Coverage Δ	Complexity Δ
#javascript	53.01% <ø> (ø)	0 <ø> (ø)	⬇️
#phpunit	65.69% <ø> (ø)	20070 <ø> (ø)	⬇️

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[codecov]

Codecov Report

Merging #35158 into stable10 will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             stable10   #35158   +/-   ##
===========================================
  Coverage       64.47%   64.47%           
  Complexity      20070    20070           
===========================================
  Files            1288     1288           
  Lines           76936    76936           
  Branches         1307     1307           
===========================================
  Hits            49606    49606           
  Misses          26949    26949           
  Partials          381      381

Flag	Coverage Δ	Complexity Δ
#javascript	53.01% <ø> (ø)	0 <ø> (ø)	⬇️
#phpunit	65.69% <ø> (ø)	20070 <ø> (ø)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 78b4819...0423f2e. Read the comment docs.

[skshetry]

This happens on waitForAjaxCallsToStartAndFinish, so, the page is already loaded but looks like jQuery is still getting parsed/downloaded. So, wherever we execute jQuery scripts from our test code, it'd be better to wait for jQuery to be available(i.e. wait for jQuery to be bound on the window). It could be implemented as following, and add the function wherever we use jquery such as waitForAjaxCallsToStartAndFinish.

function waitTillJqueryIsLoaded(Session $session) {
    // language=JS
    $script = 'function blockTillJqueryIsLoaded() {
                        if (window.jQuery) {
                            return;
                        } else {
                            setTimeout(function() { blockTillJQueryIsLoaded() }, 50);
                        }
               };
               blockTillJqueryIsLoaded();
            ';
    $session->executeScript($script);
}