I just try to be practical and make them protected so they can be called from the test class which lives in the same package. Perhaps adding a @VisibleOnlyForTesting annotation.

The reality is that these private functions are building blocks that can be easier to test. If you only test the public methods, testing gets a lot more challenging and the methods are more difficult to test and the tests classes get a lot of more complicated. You end up creating more mocks or other doubles and bending backwards.