function assertLogLevelsValues(transport, logLevels, logLevelsName = 'stderrLevels') {
  return function () {
    assume(JSON.stringify(Object.keys(transport[logLevelsName]).sort()))
      .equals(JSON.stringify(logLevels.sort()));
  };
}
Returns a function that asserts the `transport` has the specified
logLevels values in the appropriate logLevelsName member.

@param  {TransportStream} transport Transport to assert against
@param  {Array} logLevels Set of levels assumed to exist for the specified map
@param  {String} logLevelsName The name of the array/map that holdes the log leveles values (ie: 'stderrLevels', 'consoleWarnLevels')
@return {function} Assertion function to execute comparison