Add more browser tests

[funkyboy]

Following this discussion about supported platforms let's add more browser tests. The idea is to add older browser versions so we can state which platforms we support with more confidence. Here's a list of candidates:

• Opera latest
• Firefox 51
• Chrome 56
• Opera 41

cc SimonWoolf paddybyers

┆Issue is synchronized with this Jira Story by Unito

[SimonWoolf]

The idea is to add older browser versions so we can state which platforms we support with more confidence

Happy to add more platforms if that'd be useful. But to reiterate what I said in the other issue: the set of platform/browser combinations we support will always be vastly more than the set we can possibly test; we shouldn't conflate the two.

Also though -- a failure of ci-travis-all is currently useless as an indication of a regression for a PR, since it always fails due to the compatibility bugs we currently have. So spending time adding more minor variations on chrome versions is really a bit pointless if we're not paying attention to it anyway! Lets get it reliably passing first so it's actually useful -- i.e. fix all the bugs it currently exposes -- then we can start thinking about adding more platforms to it.

[funkyboy]

@SimonWoolf I agree we should fix current failing tests before adding more browsers. See this discussion for more details

[owenpearson]

Closing this as our browser testing setup has moved on quite a bit since this discussion and I'm pretty happy with the range of browsers we currently test on.