ES6 Testing Framework

Seeing as node 6.2 supports nearly all es6 features

for the code that is written purely to run on the server, is there any framework that currently supports unit testing of es6 code, I have previously used tools for transpiling to es5 for testing.

All the information i can find seems to be on the above i.e.

transpiling es6 -> es5 -> running tests.

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Are there no frameworks that support testing plain es6??

and as a sidenote: is es6 -> es5 through use of tools like babel etc safe, or are there certain es6 features that need to be avoided