Laravel: PHPUnit test fails when running and external library was added to project

I'm building an API using Laravel 5.2.

I have a POST call which references an external library added to the project. The external library is within a folder called Libraries inside the app folder.

The libraries folder is also added to the "autoload" and "classmate" keys inside the composer.json file.

"autoload": { "classmap": [ "database", "app/Libraries" ] },

The call works great but when running inside a PHPUnit test, it fails (Internal Error: 500).

The test fails right when calling the external library method.

What I'm doing wrong or forgot to setup?

via Chebli Mohamed