Cohosting tests for Uri presentation

[davidwengier]

Part of #9519 and #10603

After this, all cohost endpoints have test coverage 😁

[davidwengier]

Thought of a missing test case, added it, found a product bug! This whole testing malarky works, who knew?!

[davidwengier]

@DustinCampbell curious if you have any thoughts about the last commit? Eventually we might need something that can be used by multiple services, to control whether their endpoints should do further processing, so we can flesh this out later, I'm mainly curious if you are staunchly against me defining a record inside an interface :)

[DustinCampbell]

@DustinCampbell curious if you have any thoughts about the last commit? Eventually we might need something that can be used by multiple services, to control whether their endpoints should do further processing, so we can flesh this out later, I'm mainly curious if you are staunchly against me defining a record inside an interface :)

I'm good with the change you made. I agree that we'll need something that can be used by other services later. I have no problem with types defined inside interfaces. 😄