function splitDomCases(testFn) {
  testFn(3, '<b>begin bold<i>ita</i></b>', '<b><i>lic</i>end bold</b>');
  testFn(0, '<b>begin bold<i>&nbsp;</i></b>', '<b><i>italic</i>end bold</b>');
  testFn(6, '<b>begin bold<i>italic</i></b>', '<b><i>&nbsp;</i>end bold</b>');
}
Runs different cases of splitting the DOM.
@param {function(number, string, string)} testFn Function that takes an
    offset, firstHalfString and secondHalfString as parameters.