Improved exceptions

[mauris]

Exceptions now have better description than before.
use of \InvalidArgumentException and more categorisation of exceptions

[ghost]

Test cases evolving with improved exceptions

https://github.com/thephpdeveloper/php-queue/blob/master/test/PHPQueue/BaseTest.php#L30
https://github.com/thephpdeveloper/php-queue/blob/master/test/PHPQueue/BaseTest.php#L39
https://github.com/thephpdeveloper/php-queue/blob/master/test/PHPQueue/BaseTest.php#L118
https://github.com/thephpdeveloper/php-queue/blob/master/test/PHPQueue/BaseTest.php#L127

Can now catch the more generic [Queue|Worker]NotFoundException and no longer need to assertTest the error message.

try {
    Base::getQueue('NonExistent');
    $this->fail("Should not be able to get the Queue");  //IS SUFFICE
} catch (QueueNotFoundException $ex) {
}

Or the more pragmatic way:

/**
 * @expectedException QueueNotFoundException
 */
public function testCanFailWhenInvalidQueueNameAreGiven()
{
    //...
}

[miccheng]

Agree on using the separate test function for testing exception.

[ghost]

Maybe conclude this PR first as Sam may be busy for that.

[mauris]

Actually for PHPUnit, it is recommended we write a failing test, then write the @expectedException tags to help us test exceptions proper.

Read: http://www.phpunit.de/manual/3.2/en/writing-tests-for-phpunit.html

[miccheng]

Yeah, i was trying to keep things in the same assert block. But yes, let's do it as a separate @expectException function.