Goal: 
Perform accessibility tests for a proposed software fix in the form of a patch or merge request.
Detailed steps: 
  1. Set up prerequisites: Log in and either be ready to set up an Online testing site, or else have a Local development site and Git set up, from Common Prerequisites for Contributors. (These steps assume you will be using an online testing site.). Also, a screen reader and one or more accessibility tools from External Accessibility Resources.
  2. Choose a project to work on, either Drupal core or a contributed module, theme, or distribution that you are familiar with.
  3. Find the issues for the project, and click Advanced search. Filter to find issues with status Needs review and tagged with either "Accessibility" or "Needs accessibility review" (here is a link to search for Drupal core issues with accessibility tags). If there are no issues for your project, find another project to work on.
  4. Choose an issue to work on. Read the issue and make sure you understand the problem, what versions and browsers it applies to, and the proposed resolution (what changes are being made to what software features and behavior). If not, choose another issue.
  5. Create a new online test site to test the patch or merge request:
    • If the issue has a merge request, there should be a link in the merge request area to a preview site. See Using live previews on core merge requests for more information.
    • If the issue has a patch file, see the "Using online Drupal testing sites" section of the Setting up a test environment page to set up an online testing site. In the Project field, select the project you are testing (Drupal Core or the contributed module, theme, or distribution). For the version, select the latest development branch that the issue applies to. (Branches are listed at the bottom of the version list, and end with ".x".) Copy and paste the URL for the patch file into the Patch section (under Advanced). Then launch the site.
  6. Your task now is to test each page/feature/behavior that is changed in the patch for accessibility:
  7. Add a comment to the issue with the results of your testing (see Creating or updating an issue for details on how to do this). List the tests that you ran, tools and browsers that you used, which pages or behaviors you tested, and the results of your testing (screenshots can be helpful). If some of the tests failed, change the issue status to Needs work, and if possible, suggest ways to fix the problems. Save the comment and your status updates.