Can you point me in the right direction on how you performs tests like this?

haha; I was just thinking the same thing. 1 line of code isn't better if first response is 'whhaaat' to looking at it and you have to disect it.

...but way to use the various built-in methods.

Clever, but not sure about best practice.

Is it just me or is this part of the instructions confusing? First line is clear, 2nd is not...to me. After some testing, it seems that the reference to 'digit' is the same as the reference to 'character' in the previous line. The different verbiage makes it seem like they are two different things.

If the 9th character matches the modulus 11, the VIN is valid.
Note: If the modulus 11 of the sum is equal to 10, then the digit is "X".

Interesting tip)

+1 for the instruction on this part being confusing.

You're correct, while map works in this situation a simple For loop is more than enough.
Take the best practices with a grain of salt as they are often far from best practice in terms of readability and or efficiency.