I’m not aware of any other way to test it, so I won’t be able to help you with that. However, I would like you to do just one more thing in case you haven’t. When configuring the GPIOs to work with I2C, did you make sure that the changes where taking place? If possible, I would like you to run the cat command on these pins just to make sure that the direction is actually changing.
Let me know if you need some clarification.