Here are some test cases that involve "write" operations on wikis and databases.
Note that not all of these test cases are actually done today as part of our routine testing. This is just a list of potential tests that could benefit from, or indeed might require, production access.

• Account creation
  • Create a new account successfully (the account might not be used for any other purpose).
  • Attempt to create an account from a blocked IP, and verify that a proper error message is shown.
• Editing (wikitext)
  • Edit the wikitext of an article and submit the change successfully.
  • Attempt to edit an article from a blocked IP, and verify that a proper error is shown.
  • Attempt to edit an article that is protected (e.g. edit an extended-confirmed protected article from a non-confirmed account), and verify that a proper error is shown.
  • Make an edit that will trigger a warning message from the abuse filter, and verify that the error is shown correctly.
  • Make an edit that will trigger a blocked message from the abuse filter, and verify that the error is shown correctly.
• Editing (suggested edits)
  • Use the Suggested Edits workflow to add a new Article Description successfully.
  • Attempt to add a new Article Description from a blocked IP, and verify that a proper error message is shown. (Article Descriptions are written directly into the article on enwiki, and written to the corresponding wikidata entity for all other languages.)
  • Attempt to add a description that triggers a warning from the abuse filter, and verify that the error is shown correctly.
  • Use the Suggested Edits workflow to add a new Image Caption successfully. (Image Captions are written to the Commons structured data entity that corresponds to a File:)
  • Attempt to add a new Image Caption from a blocked IP, and verify that a proper error is shown.
  • Attempt to add a caption that triggers a warning from the abuse filter, and verify that the error is shown correctly.
  • Use the Suggested Edits workflow to add a new Image Tag successfully. (Image Tags are written to the Commons structured data entity that corresponds to a File:)
  • Attempt to add a new Image Tag from a blocked IP, and verify that a proper error is shown.
• Native Talk interface
  • Leave a message on a Talk page of another user's account, successfully.
  • Attempt to leave a message from a blocked IP, and verify that a proper error message is shown.
  • Attempt to leave a message that will trigger a warning from the abuse filter, and verify that the error is shown correctly.
• Echo notifications
  • From a different account, leave a message on the talk page of the current account, and verify that the current account receives a notification.
  • From a different account, mention the current account (via @mention) in a message on another talk page, and verify that the current account receives a notification.
  • From a different account, revert an edit made by the current account, and verify that the current account receives a notification.
  • From a different account, thank the current account for an edit that was made, and verify that the current account receives a notification.

Additional example, how would we test this T317504, if we have the constraint of testing it on test wiki, something like this needs to be checked on Russian Wikipedia