add missing TestConfig test

[zeroXbrock]

Motivation

we added a new feature w/o adding tests 🙈

Solution

• add test
• clean up some code

PR Checklist

• Added Tests
• Added Documentation
• Ran cargo +nightly clippy --workspace --lib --examples --tests --benches --all-features --locked --fix
• Ran cargo fmt --all
• Note breaking changes in PR description, if applicable
• update changelogs
  • Update CHANGELOG.md in each affected crate
  • add a high-level description in the root changelog