function getHarness( options, clbk ) {
	var opts;
	var cb;
	if ( harness ) {
		return harness;
	}
	if ( arguments.length > 1 ) {
		opts = options;
		cb = clbk;
	} else {
		opts = {};
		cb = options;
	}
	opts.autoclose = !canEmitExit;
	harness = createExitHarness( opts, cb );

	// Update state:
	getHarness.cached = true;

	return harness;
}
Returns a benchmark harness. If a harness has already been created, returns the cached harness.

@private
@param {Options} [options] - harness options
@param {Callback} [clbk] - callback to invoke when a harness finishes running all benchmarks
@returns {Function} benchmark harness