refactor(test): org application tests to own module (#18832)

Extract the application-oriented tests out to a separate module, as the
current one mixes concerns and has become a little unwieldy.

Updates a couple of tests to remove reliance on a route mapping
function when not needed.

Updates test utility import paths to absolute instead of relative.

Signed-off-by: Mike Fiedler <[email protected]>

Author: miketheman