Add unit test for FormatLabel widget

Author: openhands-agent

tests/test_widgets.py

@@ -204,3 +204,9 @@ def test_all_widgets_max_width(max_width, term_width) -> None:
             assert widget == ''
         else:
             assert widget != ''
+def test_format_label() -> None:
+    bar = progressbar.ProgressBar(widgets=[
+        progressbar.FormatLabel('Processed: %(value)d')
+    ], max_value=10)
+    for _ in bar(range(10)):
+        pass