text: Title: Cleanup: pkg/util/ipset 
  Body: As exposed in https://github.com/kubernetes/kubernetes/pull/108351 the validate logic should probably return an `error` and the test should compare the error string with a known value - to prove that it failed for the right reasons.
  
  Additionally the test could uset `t.Run()` to print a helpful name, rather than the comments tracking `// case[3]` 
  
  Easy change, good beginner case.