Would be nice to see bigger numbers, like 1 to 1000 for example

Also check for user solution length to avoid people using a pre-computed hashmap...

Trivial map/filter/reduce and factorial calculation are not novel kata ideas.

The name is a little misleading: maybe "product of factorials" instead of "factorial of factorials"? Not a huge deal, just a minor thing

You shoud put random test case and bigger number

• still no random tests
• missing edge case: 0
• since you say nothing about it in the description, n could be negative => add a note it won't be.

About the random tests:

If you look at the link I gave you, you'll see that the idea is to generate a random input and to check the result of the user's function on it against the result of a reference solution. And you do that in a loop to do like 50-100 random tests.