public function testFilterKey()
{
$array = [1, 2, 3];
$seq = new Sequence($array);
$filtered = $seq->filterKey(function ($_) {
return $_ & 1;
});
$this->assertTrue($filtered instanceof Sequence);
$this->assertEquals($array, $seq->toArray());
//check original Map is not altered
$this->assertEquals(1, $filtered->count());
$this->assertEquals(2, $filtered->get(0));
}
