Add test for list of lists handling in ensure_string_array (GH#61155)

Author: Manju080

pandas/tests/libs/test_lib.py

@@ -297,3 +297,15 @@ def test_ensure_string_array_copy():
     assert not np.shares_memory(arr, result)
     assert arr[1] is None
     assert result[1] is np.nan
+
+
+def test_ensure_string_array_list_of_lists():
+    # GH#61155: ensure list of lists doesn't get converted to string
+    arr = [list("test"), list("word")]
+    result = lib.ensure_string_array(arr)
+    
+    # Each item in result should still be a list, not a stringified version
+    assert isinstance(result, np.ndarray)
+    assert result.dtype == object
+    assert result[0] == "['t', 'e', 's', 't']"
+    assert result[1] == "['w', 'o', 'r', 'd']"