phpspec callback matcher

gistfile1.php

    function it_handles_register_command(MemberRepository $members)
    {
        $command = new MemberRegisterCommand('email', 'password', 'password');
        $members->save(Argument::that(function($member) {
            return ($member->email == 'email' && $member->password == 'password');
        }))->shouldBeCalled();

        $this->handle($command)->shouldBeAnInstanceOf(MemberRegisterCommandResponse::class);
    }