Testing the object you pass in a mocked method

Let's image we have a class:

1class EmailSender
2{
3    public function send(Email $email): void
4    {
5        // your implementation
6    }
7}

The Email class will hold the details to the email you want to send:

1class Email
2{
3    public string $template;
4 
5    public string $email;
6 
7    //...
8}

If you want to mock the EmailSender you can do something like this:

 1...
 2 
 3class EmailSenderTest extends TestCase
 4{
 5    public function testEmailSender()
 6    {
 7        $this->instance(
 8            EmailSender::class,
 9            Mockery::mock(EmailSender::class, function (MockInterface $mock) {
10                $mock->shouldReceive('send')
11                    ->withAnyArgs()
12                    ->once();
13            })
14        );
15 
16        ...
17    }
18}

The approach above you are testing if the send message is called once, but you haven`t tested if the argument provided to the method has the correct data on it.

To add checks on the object as well, you can assert it in the with for a mocked object, as:

 1...
 2 
 3class EmailSenderTest extends TestCase
 4{
 5    public function testEmailSender()
 6    {
 7        $this->instance(
 8            EmailSender::class,
 9            Mockery::mock(EmailSender::class, function (MockInterface $mock) {
10                $mock->shouldReceive('send')
11                    ->with(Mockery::on(function (Email $email) {
12                        $this->assertEquals('my-template', $email->template);
13                        $this->assertEquals('[email protected]', $email->email);
14                    })->once();
15            })
16        );
17 
18        ...
19    }
20}

This way your test is only going to pass if the Email class has expected template and email properties.