function testCompact()
{
$a = new Collection(array('a' => 3, 'b' => 2, 'c' => array(), 'd' => null));
$this->assertEquals(2, count($a->compact()));
$this->assertEquals(3, $a->compact(function ($val) {
return $val === null;
})->tap(function ($iter) {
var_dump(iterator_to_array($iter));
})->count());
}
