如何在PHP中进行某些操作后检查对象是否发生了变异？

I am writing unit test for a PSR7 implementation. I want to check if a method of MessageInterface like withProtocolVersion, do not mutate the original object.

How to check if the object is mutated after some operation in PHP?

Compare the objects strictly:

class Foo {
    public $foo = 'bar';
}

$foo = new Foo();

var_dump($foo === $foo);

$foo2 = clone $foo;
$foo2->foo = 'not bar';

var_dump($foo2 === $foo);
var_dump($foo2 === $foo2);

I'm not sure if you're using phpunit, if yes try assertSame() and assertEquals().