Axe core throws exception for wcag21a tag

[lpriyasiva]

Expectation: Axe 3.1.2 should ignore wcag21a tag
Actual: Axe 3.1.2 throws an exception if wcag21a tag is included in the ruleset

Motivation: In comply, we have rules in a standard template file. We are unable to add wcag21a as a tag in case new standards get added for it.

axe-core version: 3.1.2
axe-webdriver, extension or other integration version: X.Y.Z

Browser and Assistive Technology versions

For Tooling issues:
- Node version: XX  
- Platform:  

[WilcoFiers]

Howdy, thank you for reporting. There are currently no wcag21a rules, so that is why axe-core is throwing the error. I talked to @dylanb about this a few weeks ago and we concluded this erroring out when it finds no matching tags is probably a bit too aggressive. We'll make sure to have this work a little more gracefully.

[straker]

I believed this was fixed in #1290. Both axe.getRules(['badTag']) and axe.run({ runOnly: ['badTag'] }) do not throw errors

[chandana7393]

There is no wcag21a in Attest ruleset and also in comply Testing standards there is consistency over everywhere.Instead of wcag21a there are using wcag21aa.


Tested Environment:
Attest - 2.5.0.15720v
Comply server Url - https://comply-qa-centos-core.dequelabs.com
Comply version - v6.3.1.5792