[lib] add tests for report reducer

Summary:
After implementing operations architecture in this reducer we will not be using comparing operations vs old logic, that being said those tests should make sure that new logic will be correct

Depends on D7916

Test Plan: run tests

Reviewers: tomek, michal

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D7919