We are planning to switch to Windows 10. Is is possible to test Windows 10 before we implement it to our production environment, without having to obtain the necessary licenses upfront?

Yes, Microsoft provides the option to obtain Windows 10 Enterprise from the Technet Evaluation Center free of charge for testing purposes. With this test license, you can fully test the features for 90 days. Testing in a virtual machine is also possible. After 90 days the installation is no longer usable.

Source: Website Microsoft TechNet Evalutation Center (https://www.microsoft.com/en-us/evalcenter/evaluate-windows-10-enterprise), accessed on 09.03.2017