Really nice kata, well done.

Agree. A bit confusing description

I think the description is not complete. It should be written what is the depth of the object. There should be more examples.
I thought that the depth of this object {a: {b: {d: 1}}, f: {t: 2}} (for example) is 4, but then I realized, that the goal of this kata is to find the max depth of the object.

Thanks.

It should be specified in the Description that an Array has a depth of 0. The Example tests should not introduce new specs.

null is .. interesting, but I found out that primitive Strings are as well, in the same way that Arrays are. Well done!

Why not include undefined in the possible values? And / or less standard Objects like Sets, Maps, Dates and RegExps ? ( If you want to see the world burn, do something smart with a Proxy! :D )

There are not tests about ignores arrays in the complete tests.
i.e. This solution fails on it but can pass the final tests.