The error messages are announced to users of assistive technologies (e.g., screen readers) using appropriate ARIA roles such as aria-live="assertive" (inline) or role="alertdialog" (modal).
Error messages not announced:
This form doesn't place input error messages in an aria-live region:
Note: Possible to automatically test. An auto-test can be performed by checking if elements with e.g. role="status" or role="alert" have parent elements with valid aria-live attributes (e.g. aria-live="polite" or aria-live="assertive"), or the elements themselves have corresponding forementioned attributes. However, determining if elements without proper roles are error messages requires a human tester or AI.