public function testFilter()
 {
     // from js
     $evens = __u::filter(array(1, 2, 3, 4, 5, 6), function ($num) {
         return $num % 2 === 0;
     });
     $this->assertEquals(array(2, 4, 6), $evens, 'selected each even number');
     // extra
     $odds = __u(array(1, 2, 3, 4, 5, 6))->filter(function ($num) {
         return $num % 2 !== 0;
     });
     $this->assertEquals(array(1, 3, 5), $odds, 'works with OO-style calls');
     $evens = __u::filter(array(1, 2, 3, 4, 5, 6), function ($num) {
         return $num % 2 === 0;
     });
     $this->assertEquals(array(2, 4, 6), $evens, 'aliased as filter');
     $iterator = function ($num) {
         return $num % 2 !== 0;
     };
     $this->assertEquals(__u::filter(array(1, 3, 5), $iterator), __u::select(array(1, 3, 5), $iterator), 'alias works');
     // docs
     $this->assertEquals(array(2, 4), __u::filter(array(1, 2, 3, 4), function ($num) {
         return $num % 2 === 0;
     }));
 }