It's been six months since the question was asked, but in case someone else runs into this problem, here's what's going on. The tests check for negative numbers, and you're likely treating '-' as a digit of the number somewhere. Since '-' isn't a number/int, it gives this error. The instructions should point out negative numbers must be accounted; though really it doesn't make sense to include them given that the output can't be negative.

I believe I have arrived at a solution for the Java version of this kata. However, I am failing a test case which appears to test the method with a String -> dashatize("-");, even though the method signature calls for an int. I had even tried using an overloaded method that takes a String and then calls & returns dashatize(0) - which works in Eclipse, but no joy here on CodeWars. I am just wondering whether I am missing something or perhaps this is a glitch of some sort. Thanks in advance if you happen to see this comment and reply.

and same here... :/

My solution tests clean in Eclipse and in the preliminary tests on the site, but fails when I submit: "Should return true for a valid walk. expected: but was:". Unfortunately, I am not provided with any details as to the cause of failing the test.