Probably a dumb suggestion but I wouldn't mind seeing float numbers in here. Like, converting "0.05" to "5/100" and then "1/20" would fit this kata imo.

It is unspecified what helper actually does. And for an estimated 4 kyu ( or most solvers' estimate of 5 kyu, which I agree with more ) kata, supplying such a helper seems unnecessary. Remove that?

Speeling error "restriced" in Description#Restrictions

Speeling error "soltuion" in Tests#test_forbidden_methods

-10**15-(10**15)*1j can be written as -1e15-1e15j. I'm not sure which is more readable. - 1_000_000_000_000_000 - 1_000_000_000_000_000j is possibly the best option. Shorter is not always better.

I don't really understand what's edgy about the massive numbers; they're just big. Consider describing them as big instead of edge cases. 0 is an edge case, but there is nothing special about ±1e15±1e15j.