Are we not allowed to create a private method inside a PHPUnit file?

I have written a phpUnit file and 1 test which ran fine. I noticed that a huge chunk of the test will be reusable in my next tests, so I decided to extract a private method. and when I ran it again, I got:

"Test method "<method name>" in test class "<Test Class Name>" is not public.

Are we really not allowed to write private methods?