Additional test case for 'Logs, logs, logs!'?

Programming Go
1

I’m currently mentoring someone on the Logs, logs, logs! exercise and they have the following implementation for the WithinLimit() function:

func WithinLimit(log string, limit int) bool {
    countChar := 0
	for _ , valueString := range log {
		if valueString < 127 {
			countChar++
		}
	}
	return 	countChar < limit
}

I have two questions about this:

  1. My understanding is that this implementation is wrong. It should count all characters, not check if the number of ASCII characters is one below the limit (or less). Is that correct?
  2. If I understood correctly, is it worth it to add an extra test case for this exercise? Either one of the following two example cases would catch the issue:
	{
  		name:  "exact limit - ASCII only",
  		log:   "exercism",
  		limit: 8,
  		want:  true,
  	},
  	{
  		name:  "over limit - extra emoji",
  		log:   "exercism❗❗",
  		limit: 9,
  		want:  false,
  	},