public function testAddMultiDoesNothing()
{
$A = new ImmutableSet([1, 2, 3, 4]);
$B = $A->copy();
$A->addMulti([5]);
$A->addMulti([6, 7, 8]);
$A->addMulti([7, 8, 9]);
$A->addMulti([new Set(['a', 'b'])]);
$this->assertEquals($B, $A);
$this->assertEquals($B->asArray(), $A->asArray());
}