Yep, we (fortunately...) don't need to care about grammatical correction here.

@DennisVH: The fluff does not explain the reason for the function name. It introduces the correct requirement, but with a mismatched name that suggests the requirement may have been written incorrectly. The correct solution to the kata is "Get clarification from business." ;)

Great!, when you have suggestion mark them as such. My english is not that good I'll try to integrate that in the description

A little hacky... ;)

Looks can be deceiving.

The fluff mentions this.
the name only is there for historical reasons.

I see why it throws this exception. Output is sometimes bigger than the int.max. need to change the last charcter to 1 or 0

I think that it is implied by the return type of the function.

Instead of converting 1173245091 to 5173245091, you can always convert the former to something like 1173245191

Seems that you are returning "null"

I would like to know what I am doing wrong

With all respect I pass all the tests but one why am I failing the tests I do not understand what it is because there is description in the error message it just say expected true but was false.