function coverageClass(coveragePctg) {
  if (coveragePctg >= 75) {
    return 'high';
  }
  if (coveragePctg >= 50) {
    return 'medium';
  }
  if (coveragePctg >= 25) {
    return 'low';
  }
  return 'terrible';
}
Return coverage class for a given coverage percentage.

@api private
@param {number} coveragePctg
@return {string}