[QA] Browser testing components that disappear quickly e.g. ajax

[Jon Robson]

I have two things I want to write tests for.
1) When a user clicks on a link in alpha on mobile the page loads via
JavaScript and an ajax loader appears.

2) When a user uploads an image, after hitting submit they see a progress bar.

Both of these elements typically appear for a short period of time
before disappearing.

Using the following rule:

Then(/^I see an upload progress bar$/) do
  on(ArticlePage).progress_header_element.when_present.should be_visible
end

When I watch the test run I see that the progress_header is in fact
visible, but Watir does not find it. If I update the JavaScript so the
progress header never disappears, then the test passes.

Is there some kind of time interval for checking this sort of thing?

For reference here is the patch...
https://gerrit.wikimedia.org/r/#/c/116167/

Any ideas how to deal with this sort of browser test?