Add a value example to mock

[T-Kay]

Add a value example to mock

[whitlockjc]

This should probably be enabled via some option. Do you mind updating your PR to have a middleware option to enable this? Also, some tests would be nice as well.

[whitlockjc]

Would you mind adding a test for this?

[farrago]

This appears to do the same thing as #304, which already includes unit tests and has also had quite a bit of discussion.

Perhaps you could consider landing #304 instead of / as well as this?