Explanation
The development team missed using the with Sharing keyword in Apex classes to enforce sharing rules evaluation, and the isAccessible() method in Apex classes to check field accessibility. The with Sharing keyword ensures that the Apex code respects the sharing rules defined for the current user, while the isAccessible() method checks if the user has read access to a specific field1. The run as method in test class is used to test whether a user can perform certain actions, not to enforce permissions2. The isSharable keyword in Apex classes does not exist.