Additional test case

This adds a test case for unicode-rs#19 (which was a mismatch between forward
and reverse iterators in the original codebase).

Author: raphlinus

src/test.rs

@@ -34,6 +34,10 @@ fn test_graphemes() {
         // family emoji (more than two emoji joined by ZWJ)
         ("\u{1f468}\u{200d}\u{1f467}\u{200d}\u{1f466}",
          &["\u{1f468}\u{200d}\u{1f467}\u{200d}\u{1f466}"]),
+        // cartwheel emoji followed by two fitzpatrick skin tone modifiers
+        // (test case from issue #19)
+        ("\u{1F938}\u{1F3FE}\u{1F3FE}",
+         &["\u{1F938}\u{1F3FE}", "\u{1F3FE}"]),
     ];
 
     for &(s, g) in TEST_SAME.iter().chain(EXTRA_SAME) {