rework TestShelvesSerializer.setUpTestData (#16037)
rework TestShelvesSerializer.setUpTestData (#16037)


wagnerand/addons-server,wagnerand/addons-server,bqbn/addons-server,diox/olympia,mozilla/olympia,diox/olympia,bqbn/addons-server,diox/olympia,mozilla/addons-server,wagnerand/addons-server,bqbn/addons-server,mozilla/olympia,bqbn/addons-server,diox/olympia,mozilla/addons-server,mozilla/olympia,mozilla/addons-server,mozilla/addons-server,wagnerand/addons-server,mozilla/olympia