Add unit tests to param-validator

Background / User story

This is a follow up to #1558 (closed), where a bug was discovered in the IPM code that was introduced by a change in #1512 (closed).

Essentially: we modified a bit of code, and that introduced a bug. Nothing to exceptional here, but:

The bug was introduced in utility functions that are core of the business logic of the IPM system
These functions are mostly simple pure functions

These functions should have unit test to guarantee that we don't break the IPM logic.

Add unit tests to the functions in src/ipm/background/param-validator.ts

npm run test is green 🟢 No change to runtime code so there is nothing to QA.