Add html-proof for automated testing

[Chilipp]

This should have been done before, but I forgot about it.

As we are facing a lot of broken links, this PR adds a checker using html-proofer that particularly checks for broken links. Note that it unfortunately does not work for setting the baseurl or url in the _config.yml, so I needed to exclude it in the .circleci/_config.yml file.

closes #124, closes #152, closes #153 and solves several other broken links

[vsoch]

I'm a little bit biased, but I've used html-proofer in the past and it tends to have issues because it isn't able to retry, whistlist, or do functionality that we would need. Instead of html-proofer I want to suggest the urlstecher / urlchecker-action:

https://github.com/urlstechie/urlchecker-action

it has huge ability for customization, and includes all the features that html-proofer was lacking (at least when I used it). I'm one of the developers on the project, so I can be responsive to help requests, issues, etc. There is also a nice folder of example github workflow templates to start with.

[vsoch]

And some background is here USRSE/usrse.github.io#171 - we literally went through the same steps of having html-proofer to run on travis/circle, and then it was a pain because ephemeral timeouts, etc. would fail the PR.

[Chilipp]

Nice @vsoch! I did not know this. Having you as the developer of the testing library onboard is already reason enough for me to use your library due to the better support 😉 would you mind changing the files in this PR to set it up for url-checker? Or shall we do this in a new PR?

[vsoch]

If it's okay with you, I think a new PR should be done - this one has quite a bit going on (unless it wasn't rebased?)

[Chilipp]

alright, then let's close this, I make a cherry-picked one for the fixes (788ad47, 21bca57, 97b7387, 082bf52 and f31d7f1) and you make a new one for implementing the URL checker. Alright?

[vsoch]

If you are going to close, let's just leave it open so I can make sure they work the same. Also, I'm going to bed soon so I hope you don't expect this soon! Feel free to jump in and do the PR if you don't want to wait for me :)

[Chilipp]

Sure, it must be really late across the ocean, no worries :D I'd at least already implement the fixes, the url checker can wait until you're awake again, I guess (as the broken links where identified already). Thanks a lot @vsoch!

[Chilipp]

alright. I merged the master branch and fixed the new problems. So this is ready to be reviewed

[vsoch]

My mistake! I did a grep and two showed up (one inside, one outside the _site folder). What about the 404 page url, that was the other url that was missing:

orry, but the page you were trying to view does not exist --- perhaps you can try searching for it below.
Sorry, but the page you were trying to view does not exist.

<script>
  var GOOG_FIXURL_LANG = 'en';
  var GOOG_FIXURL_SITE = '{{ site.url }}'
</script>
<script src="https://linkhelp.clients.google.com/tbproxy/lh/wm/fixurl.js">
</script>

I'm not sure https://linkhelp.clients.google.com/tbproxy/lh/wm/fixurl.js is online anymore?

[vsoch]

Tests pass, so all must be good :)

[Chilipp]

true, I excluded 404.html in the check. I'll add your 404.html from e7682cf

[Chilipp]

done, thanks @vsoch!

[Chilipp]

feel free to approve and merge this PR then @vsoch

[Chilipp]

done @vsoch, these issues existed already in the original README 😅

[vsoch]

And I should probably stop looking, now I just feel bad :) I think it’s good for squash and merge and any remaining details can be addressed later! Perfection is the enemy of the good, something something.

[Chilipp]

thanks @vsoch 😆