Add Behat step to verify WCAG A and WCAG AA compliance

Initialise behat without the new --axe flag: php admin/tool/behat/cli/init.php Note the command given to execute Behat Run behat on the new tests, using the correct tag: php admin/tool/behat/cli/run.php --tags=@accessibility Confirm that you see the following output at the top : Run optional tests: - Accessibility: No Confirm that all steps pass Re-initialise behat with the --axe flag: php admin/tool/behat/cli/init.php --axe Run behat on the new tests, using the correct tag: php admin/tool/behat/cli/run.php --tags=@accessibility Confirm that you see the following output at the top : Run optional tests: - Accessibility: Yes Confirm that all steps pass Open " auth/tests/behat/login.feature " in your preferred editor Find the @_accessibility feature at the bottom of the file and add a new line: Then the page should meet accessibility standards with "cat.semantics" extra tests Run behat on the new tests, using the correct tag: php admin/tool/behat/cli/run.php --tags=@accessibility Confirm that the final step fails with some useful information For example: 001 Scenario: Login page must be accessible # /Users/nicols/Sites/moodles/sm/moodle/auth/tests/behat/login.feature:59 Then the page should meet accessibility standards with "best-practices, cat.semantics" extra tests # /Users/nicols/Sites/moodles/sm/moodle/auth/tests/behat/login.feature:64 Accessibility violations found: 1 violations of 'Ensures the main landmark is at top level' (severity: moderate) - The main landmark is contained in another landmark.: div[role="main"]     1 violations of 'Ensure that the page, or at least one of its frames contains a level-one heading' (severity: moderate) - Page must have a level-one heading: html     (Behat\Mink\Exception\ExpectationException)   1 scenario (1 failed) 5 steps (4 passed, 1 failed) 0m7.71s (48.52Mb)