Use Hamcrest matchers where possible

[basil]

While testing an unrelated change recently, I tripped over these assertions with an unhelpful error message. This PR should improve the error message when these assertions fail.

Testing done

Deliberately tripped the assertions and saw better error messages after this PR.

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed

[daniel-beck]

Thanks!