Usability testing is generally done with outside users. That is, people who are not part of the organisation which owns the site. They should also not be familiar with the content of the site being tested. The same should be true for accessibility. Yet I know some organisations will check with a handy blind employee and consider that as adequate accessibility user testing.
It is not practical or best practice to use disabled people from within your organisation to test a website. While they may be able to contribute useful feedback, their familiarity with the organisation and the content of the site will mean the experience will not be that of a ‘real’ external user.
They may also feel constrained by their position within the organisation from freely responding in a test.
Accessibility testing requires a range of potential disabled users with a variety of impairments and using different assistive technologies in their everyday situations. It is unlikely that most organisations include a full range of disabled people on staff anyway, so results from testing with a limited range of people with a limited range of impairments and technologies will not give the best outcomes.
Achieving accessibility on the Web requires organisational commitment, which means sound policy, training and accountability, an understanding of standards and best practice, good technical backup and an acceptance of universal design principles and the reasons for making a web site accessible in the first place. Real world testing is an essential part of the mix in achieving accessibility.
