Bug 1598876 - Fix intermittent link test failure

[gvn]

Run mach test discovery_render and confirm exit code of 0. (Try this several times.)

[Mardak]

The test was making sure top sites gets rendered as well as the link getting rendered, so this change makes it only test the latter. If the link is getting delayed, you can wrap the querySelector with await ContentTaskUtils.waitForCondition just like what's done for topSites.

[ScottDowne]

I also wonder if we can instead of waiting and checking the text, just check for the href, and not the text content, thus it wouldn't need to be waiting for fluent. (we're not testing fluent anyway)

thoughts?

[ScottDowne]

Was thinking about this more. I think maybe ideally we have a test layout for this, so we don't have fluent strings being used here at all. (assuming that's the issue, which I'm only about 80% sure of)