freeCodeCamp: Bug: Avoid Mutations and Side Effects Using Functional Programming needs to validate the global variable is used in the incrementer function

While reviewing a PR (#39363) that fixes a separate issue on the [Avoid Mutations and Side Effects Using Functional Programming](Avoid Mutations and Side Effects Using Functional Programming) challenge, I noticed the following test does not validate that the value returned from the incrementer function returns a value that is one larger than the fixedValue global variable’s value.

  - text: Your <code>incrementer</code> function should return a value that is one larger than the <code>fixedValue</code> value.
    testString: const newValue = incrementer(); assert(newValue === 5);

A user can simply write the following and pass the challenge without even using the fixedValue variable in the code.

var fixedValue = 4;

function incrementer () {
  // Only change code below this line
   return 5;
  // Only change code above this line
}

I suggest adding a third test, so that we set the value of fixedValue to a different value before calling the function. However, since the user could technically write const fixedValue = 4; instead of var fixedValue = 4;, one way of approaching this would be to use an IIFE: like the following:

  - text: Your <code>incrementer</code> function return a value based on the global `fixedValue` variable value.
    testString: |
      (function() {
       const fixedValue = 10;
       const newValue = incrementer();
       assert(fixedValue === 10 && newValue === 11);
      })()

Before adding a help wanted label, I am looking for feedback from others about this approach to fixing the challenge.