@alishahenderson, thanks for your comment on how to carry out accessibility testing. And I do agree with you that the best way of doing accessibility testing for a site is to make a real people with disabilities access the site. But this doesn’t help when the product is in staging. Because it will be inspected by a QA person, who reports if there are any issues and to make it more clear the question was to en-light QA people who would like to add accessibility testing as a new skill set with possible resources.
Since you have mentioned about PAS 78, it is a best practice guide and it provides advice on issues with accessibility. They have to be familiar with WCAG 2.0 as well. Also found this guide https://dojo.ministryoftesting.com/dojo/lessons/30-days-of-accessibility-testing, it should definitely help anyone to kick start their accessibility career