Testing mails in Laravel 4 is a bit of a weak spot. You can say Mail::shouldReceive('send')->once()... but specifying everything the method should receive in terms of arguments as well as asserting that the closure sets the recipient and subject correctly is tedious at best. This SO answer shows an example of how to unit test a mail being sent.

Mocking classes and defining what methods they should receive is easy.

I had a problem recently where I wanted to use PHPUnit to test what was being passed to a function. We're talking about a several hundred line string with a current timestamp, so simply using $mock->shouldReceive('method')->with('parameter string') wouldn't work.