Add an imp test for checking deposit collection and refunds

[lehins]

Description

I wanted to convince myself that deposits are correctly collected an refunded, so I decided to add a test for it.

Checklist

• Commits in meaningful sequence and with useful messages.
• Tests added or updated when needed.
• CHANGELOG.md files updated for packages with externally visible changes.
  NOTE: New section is never added with the code changes. (See RELEASING.md).
• Versions updated in .cabal and CHANGELOG.md files when necessary, according to the
  versioning process.
• Version bounds in .cabal files updated when necessary.
  NOTE: If bounds change in a cabal file, that package itself must have a version increase. (See RELEASING.md).
• Code formatted (use scripts/fourmolize.sh).
• Cabal files formatted (use scripts/cabal-format.sh).
• CDDL files are up to date (use scripts/gen-cddl.sh)
• hie.yaml updated (use scripts/gen-hie.sh).
• Self-reviewed the diff.

[teodanciu]

Looks good to me, just some minor comments