The "Operators" section only mentions 4 binary operators to implement (addition, subtraction, multiplication, division) but doesn't mention a unary operator (negation). It is only casually implied in the "whitespace" section when it talks about "negating parentheses".

The public tests also don't contain any case that uses this unary operator.

If the function is not gonna be tested against decimal numbers,
it should be explicitely stated in the kata's description.

Also, I don't find it correct to divide tests in these stages.
It gives too much information, especially when you add in
OverZealous' tests (which would fall into a "special" stage).

IMO you should divide them into "present fits" and "present doesn't fit".