instruction: Write Go code to go by example: string functions
output: ```text
   p("Contains: ", s.Contains("test", "es"))
   p("Count: ", s.Count("test", "t"))
   p("HasPrefix: ", s.HasPrefix("test", "te"))
   p("HasSuffix: ", s.HasSuffix("test", "st"))
   p("Index: ", s.Index("test", "e"))
   p("Join: ", s.Join([]string{"a", "b"}, "-"))
   p("Repeat: ", s.Repeat("a", 5))
   p("Replace: ", s.Replace("foo", "o", "0", -1))
   p("Replace: ", s.Replace("foo", "o", "0", 1))
   p("Split: ", s.Split("a-b-c-d-e", "-"))
   p("ToLower: ", s.ToLower("TEST"))
   p("ToUpper: ", s.ToUpper("test"))
  }
  ```