function validate( opts, options ) {
	if ( !isObject( options ) ) {
		return new TypeError( format( 'invalid argument. Options argument must be an object. Value: `%s`.', options ) );
	}
	if ( hasOwnProp( options, 'iterations' ) ) {
		opts.iterations = options.iterations;
		if (
			!isPositiveInteger( opts.iterations ) &&
			!isNull( opts.iterations )
		) {
			return new TypeError( format( 'invalid option. `%s` option must be a positive integer or null. Option: `%s`.', 'iterations', opts.iterations ) );
		}
	}
	if ( hasOwnProp( options, 'repeats' ) ) {
		opts.repeats = options.repeats;
		if ( !isPositiveInteger( opts.repeats ) ) {
			return new TypeError( format( 'invalid option. `%s` option must be a positive integer. Option: `%s`.', 'repeats', opts.repeats ) );
		}
	}
	if ( hasOwnProp( options, 'before' ) ) {
		opts.before = options.before;
		if ( !isString( opts.before ) ) {
			return new TypeError( format( 'invalid option. `%s` option must be a string. Option: `%s`.', 'before', opts.before ) );
		}
	}
	if ( hasOwnProp( options, 'after' ) ) {
		opts.after = options.after;
		if ( !isString( opts.after ) ) {
			return new TypeError( format( 'invalid option. `%s` option must be a string. Option: `%s`.', 'after', opts.after ) );
		}
	}
	if ( hasOwnProp( options, 'asynchronous' ) ) {
		opts.asynchronous = options.asynchronous;
		if ( !isBoolean( opts.asynchronous ) ) {
			return new TypeError( format( 'invalid option. `%s` option must be a boolean. Option: `%s`.', 'asynchronous', opts.asynchronous ) );
		}
	}
	return null;
}
Validates function options.

@private
@param {Object} opts - destination object
@param {Options} options - options to validate
@param {string} [options.before] - setup code
@param {string} [options.after] - cleanup code
@param {(PositiveInteger|null)} [options.iterations] - number of iterations
@param {PositiveInteger} [options.repeats] - number of repeats
@param {boolean} [options.asynchronous] - boolean indicating whether a snippet is asynchronous
@returns {(Error|null)} error or null

@example
var opts = {};
var options = {
    'iterations': 1e7,
    'repeats': 5
};
var err = validate( opts, options );
if ( err ) {
    throw err;
}