I grew up speaking Punjabi but I only learned how to write it from my time in Punjabi 101.
I found the challenge process to be very pleasant because once I met with my instructor and heard from him that he thought I knew the material, I had about four further email conversations with him and then wrote the challenge exam. After initially asking my instructor about it he did most of the work in getting permission from the head of the department. The faculty does a great job of setting things up and setting up an exam date that best suits your interests. The only work I had to do was to prepare to write the exam.
I would recommend that other students challenge courses if they are confident in their knowledge of the course.