    {
        $h = PersistentArrayMap::empty(new ModuloHasher(), new SimpleEqualizer());
        $h2 = $h->put(null, 'test');

        self::assertEquals(null, $h->find(null));
        self::assertEquals(0, $h->count());
        self::assertFalse($h->contains(null));
        self::assertEquals('test', $h2->find(null));
        self::assertEquals(1, $h2->count());
        self::assertTrue($h2->contains(null));
    }

    public function testPutKeyValue(): void
    {