tests: add actionable error test for mismatched closing tag in markup

tests/test_markup_error_message.py

@@ -0,0 +1,12 @@
+import pytest
+from rich.text import Text
+from rich.errors import MarkupError
+
+def test_invalid_markup_message_is_actionable_mismatched_close():
+    bad = "[bold]hello[/italic]"  # mismatched closing tag should raise
+    with pytest.raises(MarkupError) as exc:
+        Text.from_markup(bad)
+
+    msg = str(exc.value).lower()
+    # keep the assertions flexible so they work with current Rich messaging
+    assert any(word in msg for word in ("invalid", "mismatch", "closing", "end tag"))