Fix flaky specs in backend/spec/features/admin/users_spec.rb

[spaghetticode]

(This is a reopening for PR #3061 closed by mistake)

These specs are failing often on circleCI builds.

The added expectation ensures that the click toggled the table header HTML.
This has the double benefit to ensure HTML is consistent and leaves more time
to successfully verify the flaky expectation:

expect(text_match_1).to appear_before text_match_2

Also, the within_table in the second example must be splitted in order to get
green specs. This is seems to be caused by rack_test not being able to detect
updates inside the selected HTML block after a page reload.

Re-selecting the HTML block with a second within_table does the job.

Checklist:

• I have followed Pull Request guidelines
• I have added a detailed description into each commit message
• I have updated Guides and README accordingly to this change (if needed)
• I have added tests to cover this change (if needed)
• I have added a CHANGELOG entry for this change (if needed)

[kennyadsl]

@spaghetticode maybe we should change the first commit message? Or are we still uncertain it will fix?

[spaghetticode]

@kennyadsl I'm still kind of uncertain.

I mean, there was no real reason in the first place for these specs to be broken, in fact most of the time they were green anyway... apart from the real issue I fixed with the second commit (which anyway was not relevant for the original appear_before failing check, as appear_before uses the unscoped page.body) I could not find something deterministic in the failures.

I think only the future can make us certain about this.

[kennyadsl]

Thanks @spaghetticode

[kennyadsl]

@solidusio/core-team can we have another review here, please?

[tvdeyen]

Thanks!