tr: correctly detected matched [:upper:]

tr detects if a class in set2 is matched by a class at the correct position in set1 after it has expanded everything before the class in both sets:

So

tr 'abcd[:upper:]' 'a-d[:lower:]'

should not fail

tests/by-util/test_tr.rs

@@ -1375,6 +1375,13 @@ fn check_class_in_set2_must_be_matched_in_set1() {
     new_ucmd!().args(&["-t", "1[:upper:]", "[:upper:]"]).fails();
 }
 
+#[test]
+fn check_class_in_set2_must_be_matched_in_set1_right_length_check() {
+    new_ucmd!()
+        .args(&["-t", "a-z[:upper:]", "abcdefghijklmnopqrstuvwxyz[:upper:]"])
+        .succeeds();
+}
+
 #[test]
 fn check_set1_longer_set2_ends_in_class() {
     new_ucmd!().args(&["[:lower:]a", "[:upper:]"]).fails();