add test to fix coverage; use "Optional"

dp_wizard/app/dataset_panel.py

@@ -1,4 +1,5 @@
 from pathlib import Path
+from typing import Optional
 
 from shiny import ui, reactive, render, Inputs, Outputs, Session
 
@@ -102,7 +103,7 @@ def _on_private_csv_path_change():
         private_csv_path.set(input.private_csv_path()[0]["datapath"])
 
     @reactive.calc
-    def csv_column_mismatch_calc() -> tuple[set, set] | None:
+    def csv_column_mismatch_calc() -> Optional[tuple[set, set]]:
         public = public_csv_path()
         private = private_csv_path()
         if public and private:

tests/utils/test_csv_helper.py

@@ -10,6 +10,7 @@
     read_csv_ids_labels,
     read_csv_ids_names,
     get_csv_names_mismatch,
+    get_csv_row_count,
 )
 
 
@@ -24,6 +25,13 @@ def test_get_csv_names_mismatch():
         assert just_b == {"d"}
 
 
+def test_get_csv_row_count():
+    with tempfile.TemporaryDirectory() as tmp:
+        path = Path(tmp) / "a.csv"
+        path.write_text("a,b,c\n1,2,3")
+        assert get_csv_row_count(path) == 1
+
+
 # We will not reference the encoding when reading:
 # We need to be robust against any input.
 @pytest.mark.parametrize("write_encoding", ["latin1", "utf8", "utf-8-sig"])