Add assertSentTo shorthand

[jasonmccreary]

An easy, but strong assertion when testing mail is to assert that a particular mailable was sent to a specific email address.

Currently to do this, you need to write out this logic and wrap it in a closure. The following is as trim as you can get:

Mail::assertSent(MeetingMinutes::class, fn ($mail) => $mail->hasTo($user->email));

With this PR, you may now simply write:

Mail::assertSentTo(MeetingMinutes::class, $user->email);

In addition, you may also pass an array as the second argument to assert a mailable was sent to multiple users. For example:

Mail::assertSentTo(MeetingMinutes::class, ['taylor@...', 'dries@...', 'jess@...']);

An assertQueuedTo is included for symmetry.

[jasonmccreary]

If merged, I'm glad to submit a fast-follow PR to add the negative assertions (i.e. assertNotSentTo and assertNotQueuedTo)

[taylorotwell]

Could you just see if the second argument given to assertSent is a string?

[jasonmccreary]

@taylorotwell, you could. This method is already overloaded though. So be able to pass a closure, int, string, array, or null feels bloated, imo.

[jasonmccreary]

@taylorotwell, I realized assertSentTo was an old assertion (5.4), so have unified everything under assertSent and assertQueued. It has 3 different paths based on the second argument, but the code is straightforward and tested.

I also added this feature to assertNotSent and assertNotQueued.

[jasonmccreary]

The failing tests relate to RedisQueue. Given these are failing on several other PRs, I'm going to assume this is CI related and not my code. 😅