public function testFoldLeftRight() { $map = new Map(array('a' => 'b', 'c' => 'd', 'e' => 'f')); $rsLeft = $map->foldLeft('', function ($a, $b) { return $a . $b; }); $rsRight = $map->foldRight('', function ($a, $b) { return $a . $b; }); $this->assertEquals('bdf', $rsLeft); $this->assertEquals('bdf', $rsRight); }