libstd: Add unit tests for slice_shift_char

src/libstd/str.rs

@@ -3618,6 +3618,18 @@ mod tests {
         assert!(!"   _   ".is_whitespace());
     }
 
+    #[test]
+    fn test_slice_shift_char() {
+        let data = "ประเทศไทย中";
+        assert_eq!(data.slice_shift_char(), (Some('ป'), "ระเทศไทย中"));
+    }
+
+    #[test]
+    fn test_slice_shift_char_2() {
+        let empty = "";
+        assert_eq!(empty.slice_shift_char(), (None, ""));
+    }
+
     #[test]
     fn test_push_byte() {
         let mut s = ~"ABC";