[web] improve error handling in queries tests

Summary:
Context in https://phab.comm.dev/D11175#inline-67962

Depends on D11175

Test Plan:

1. Run tests
2. Set dbModule to null and check if descriptive error is visible

Reviewers: marcin, michal

Reviewed By: marcin

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11241