refactor integration tests with more useful helper functions

Refactor integration test to vastly reduce amount of redundant code, and discuss optimisations in the PR.

Start by locating the integration tests and identifying repeated setup or assertion code. Review the existing helpers before deciding which reusable functions would reduce duplication, then run the integration test suite to confirm behavior is unchanged. Done means the redundant code is reduced and any optimization discussion is captured in the pull request.

Written by the indexing model from the issue text.