Use this instead of:

public class AgeDiff

{

public static String CalculateAge(int birth, int yearTo)

{

//your code

}

}

ugh rookie mistake! thank you!

You need to return your output and not print it to the console. All katas on this website work like this. Returning the value, means the value is retained from that function call. The value retained can be checked and checked for equality against the expected answer. Printing to the console is hard to check for equality. "None" is the default value when nothing is returned.

Test Results:
Basic tests
Log
You are 4 years old.
None should equal 'You are 4 years old.'

I am not sure what this means.