Great update from @dkayiwa on the Platform Team call today:
The Platform Team folks have gone through all the Platform 2.4.0 REST-WS endpoint tests in this spreadsheet, and they have identified all the ones that already have test coverage. This uncovered that 14 of 79 API use cases still need automated test coverage. 
You can see how in the spreadsheet, they have linked the API cases to the specific area with the test coverage; these examples can be used to assist contributors who want to work on the remaining coverage gaps:
@christine @kdaud @sharif - what do you think, should we create Jira Issues for each of the 14 remaining things that still need coverage?