public function testOffsetUnset()
{
$arr = ['a' => '111', 'b' => '222'];
$hash = new HashMap($arr);
$this->assertTrue(isset($hash['a']));
unset($hash['a']);
$this->assertFalse(isset($hash['a']));
$this->assertTrue(isset($hash['b']));
$hash->offsetUnset();
$this->assertFalse(isset($hash['b']));
}