License
AltTester Unity SDK is licensed under the GNU General Public License v3.0. This means that the end user has the freedom to use, share and modify the software. It’s a copyleft license, which means that if any derivative work must be distributed, it should be distributed under the same or equivalent license terms. As long as it’s added to the development build and not distributed, it has no restrictions for the end user.
The GPL license type allows you to use this software internally in your company, without any obligations (no need to be copyright holders for the Unity engine).
The only obligation you have regarding this open source software is related to distribution. If you want to distribute AltTester Unity SDK, or some parts of it you have to make sure you distribute it under the same license terms. For example, if you plan to release a app containing AltTester Unity SDK, then you’d have to apply the same GPL3 terms to your app. Otherwise, if you only use it for developing and testing your app, you don’t have any obligations.