added new test (for rosetta)

tests/results/17

@@ -0,0 +1,20 @@
+>>> s = 'abcdefgh'
+>>> n, m, char, chars = 2, 3, 'd', 'cd'
+>>> # starting from n=2 characters in and m=3 in length;
+>>> s[n-1:n+m-1]
+'bcd'
+>>> # starting from n characters in, up to the end of the string;
+>>> s[n-1:]
+'bcdefgh'
+>>> # whole string minus last character;
+>>> s[:-1]
+'abcdefg'
+>>> # starting from a known character char="d" within the string and of m length;
+>>> indx = s.index(char)
+>>> s[indx:indx+m]
+'def'
+>>> # starting from a known substring chars="cd" within the string and of m length.
+>>> indx = s.index(chars)
+>>> s[indx:indx+m]
+'cde'
+>>>