this seems to be a recurring theme in many of these kata as of late; saw numerous issues reported and was afraid I would start working on a solution and encounter a test case with a negative number in it, so decided to check discussions before starting just in case.

There is a test case which is trying to sum empty strings like 'test.assert_equals(sum_strings("", ""), "0")', this contradicts with the description of the kata

'Given the string representations of two integers ...'
'A string representation of an integer will contain no characters besides the ten numerals "0" to "9".'

Empty string is not a string representation of an integer.