public function testFlipped()
{
$f = function ($a, $b, $c) {
return $a . $b . $c;
};
$flippedF = flipped($f);
$this->assertEquals('cba', $flippedF('a', 'b', 'c'));
$flippedF = call_user_func(flipped, $f);
$this->assertEquals('cba', $flippedF('a', 'b', 'c'));
$this->assertEquals('\\nspl\\f\\flipped', flipped);
}