Do I need both automated and manual accessibility testing?

The short answer is yes, and the following article explains why.

Automated

Automated tests are integral when identifying accessibility errors on a technical level, and are incredibly important when developing or maintaining a website. Automated accessibility testing alerts you to errors like:

• Form fields - Automated tests make sure that all entry fields have labels.
• Color - Automated tests verify that color combinations in a text are used appropriately.
• Links - Automated testing quickly determines that all links are functioning as they are supposed to.

While the Accessibility feature of the Siteimprove Intelligence Platform detects many errors, there are some tests that can only be done manually.

Manual

Manual testing evaluates websites using a combination of keyboard-only interactions, assistive computer technologies, and web browser plug-ins to determine the accessibility of the site. While automated testing accounts for many of the WCAG 2.0 criteria, manual testing accounts for errors software can’t, like:

• Presence of informative page titles - Siteimprove manual testers make sure the page title is unique, meaningful, and concise. Page titles are what is visible in tabs or bookmarks and should be appropriate to the page content and/or task.
• “Skip navigation” option - Manual tests ensure that the option to skip repeated navigational elements is present and correct. 
• HTML5 and WAI-ARIA elements - These aren’t required, but are a best practice. Manual testers can check to make sure they are being used correctly.

Combining manual and automated testing gives a more balanced and comprehensive approach to compliance. Automated testing complements manual testing by identifying coding errors that do not need human verification, saving both time and cost.

Semi-automated

We have built an assisted workflow inside the platform where users are guided through a step-by-step review process to evaluate the content on their website that could potentially be problematic from an accessibility perspective. There are potential issue reviews for HTML5 and ARIA code, text, images, and videos, etc. For further information please see the article "Accessibility NextGen: Reviewing Potential Issues".