Theory data in tests should include expected output

[RPM1984]

Currently we use theory data to control assertions, e.g here

This leads to some 'magic code' / checks, e.g:

if (id == 1)
{
    // some assertion
}

A better approach would be to setup the data in the controller/models via the tests (not hardcoded internally), and have the theory data include the expected model.

Then the assertions become a simple equality check on the JSON output.