Collections\Tests\Dictionary\FilterTest::test_filter PHP Method

    public function test_filter()
    {
        $d = (new Dictionary('string', 'int'))->add('a', 1)->add('b', 2)->add('c', 3)->add('d', 4);
        $subset = $d->filter(function ($k, $v) {
            return $v % 2 == 0;
        });
        //original is unchanged
        $this->assertEquals(4, $d->count());
        //new has 2
        $this->assertEquals(2, $subset->count());
        //new contains b and d
        $this->assertEquals(2, $subset->get('b'));
        $this->assertEquals(4, $subset->get('d'));
        //new is missing a and c
        $this->assertFalse($subset->exists('a'));
        $this->assertFalse($subset->exists('c'));
    }