Unit test fails when running and external library was added

Hello,

I'm building an API using Laravel 5.

I have a POST call which calls 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.

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?