[10.x] Call renderForAssertions in all Mailable assertions

[jamsch]

In the Laravel docs for Mail -- https://laravel.com/docs/10.x/mail the following code snippet is shown:

use App\Mail\InvoicePaid;
use App\Models\User;
 
public function test_mailable_content(): void
{
    $user = User::factory()->create();
 
    $mailable = new InvoicePaid($user);
 
    $mailable->assertFrom('jeffrey@example.com');

The $mailable->assertFrom('jeffrey@example.com'); example here will fail the test because the mailable's render() hasn't been called yet. I noticed in the PR #47728 - the renderForAssertions function was called for assertHasSubject but I could not see why this isn't being called for the other Mailable assertion functions, such as assertFrom taken from the docs.

So, in summary I've added the renderForAssertions to the following functions:

$mailable->assertFrom("");
$mailable->assertTo("");
$mailable->assertHasCc("");
$mailable->assertHasBcc("");
$mailable->assertHasReplyTo("");
$mailable->assertHasTag("");
$mailable->assertHasMetadata("");

Which will no longer mean that the user needs to call a specific $mailable->assertHasSubject() or $mailable->assertSeeInHtml() before being able to call the above methods.

[jamsch]

PR should be ready. Just a note though: many of the tests have the same mailer container class stub which may warrant some DRY refactoring.

[tmont]

FYI this is a bit of a (minor) breaking change, as it kind of drastically changes behavior of merely asserting that a Mailable has a from address or something. Now it forces a render of the entire Mailable for every assertion which may be unwanted during a testing environment (for performance reasons, for example).

Part of my email rendering process involves inlining CSS which is not something I care about nor want during a unit test, and this change forces that to happen at times when it's not needed.