Extending an existing Plugin class results in Class not Found PHP Fatal Error I am trying to create my own Plugin that extends an existing Plugin class.
I can extend the base class and everything is fine.
However, if I extend a existing Plugin class, I get a Class not Found error.

e.g.

&lt;?php

namespace Drupal\my_module\Plugin;

use Drupal\contrib_module\Plugin\ClassA;

class MyClass extends ClassA {
  public function implement() {}
}


The error I am getting would be
Class 'Drupal\contrib_module\Plugin\ClassA' not found in /var/www/project/web/modules/custom/my_module/src/Plugin/MyClass.php on line 7

Any Thoughts guys?
There is no D8 commerce_usps module yet. I found a development version on github, I pressume you're using this one. 

The use statement uses the following structure use [namespace]\[classname]

So your use statement needs to be

use Drupal\commerce_usps\Plugin\Commerce\ShippingMethod\USPS

class ForExample extends USPS { ...