public function testAllowsFunctionalMapping()
{
$this->coll->merge(array('number_1' => 1, 'number_2' => 2, 'number_3' => 3));
$mapped = $this->coll->map(function ($key, $value) {
return $value * $value;
});
$this->assertNotEquals($mapped, $this->coll);
$this->assertEquals(array('number_1' => 1, 'number_2' => 4, 'number_3' => 9), $mapped->getAll());
}