public function testFilter()
{
$map = new Map(array('a' => 'b', 'c' => 'd', 'e' => 'f'));
$newMap = $map->filter(function ($v) {
return $v === 'd';
});
$this->assertNotSame($newMap, $map);
$this->assertCount(3, $map);
$this->assertCount(1, $newMap);
$this->assertEquals(array('c' => 'd'), iterator_to_array($newMap));
}
