add ligature test cases to word_to_titlecase

Author: Rachit2323

library/alloctests/tests/str.rs

@@ -1922,6 +1922,21 @@ fn word_to_titlecase() {
         expected.push_str(&str::repeat("a", 510));
         expected
     });
+
+    // LJ ligatures and title-case characters.
+    // Lj is already a title-case letter, so it stays as the first char.
+    assert_eq!("Ljj".word_to_titlecase(), "Ljj");
+    assert_eq!("LjJ".word_to_titlecase(), "Ljj");
+    // l is the first cased char (uppercases to L), Lj lowercases to lj.
+    assert_eq!("lLjfi".word_to_titlecase(), "Lljfi");
+    assert_eq!("LLjfi".word_to_titlecase(), "Lljfi");
+
+    // LJ ligatures: lower=lj (U+01C9), upper=LJ (U+01C7), title=Lj (U+01C8).
+    // ß decomposes to "Ss" in title case (first char) but stays ß elsewhere.
+    assert_eq!("ßljLJLj".word_to_titlecase(), "Ssljljlj");
+    assert_eq!("ljLJLjß".word_to_titlecase(), "Ljljljß");
+    assert_eq!("LJLjßlj".word_to_titlecase(), "Ljljßlj");
+    assert_eq!("LjßljLJ".word_to_titlecase(), "Ljßljlj");
 }
 
 #[test]