Refine waterfall validation and test assertions

Agent-Logs-Url: https://github.com/sdpython/teachpyx/sessions/e6e8e7c7-c0a1-47b3-9763-5ebb04affcb9

Co-authored-by: xadupre <22452781+xadupre@users.noreply.github.com>

Author: Copilot

_unittests/ut_tools/test_pandas.py

@@ -30,18 +30,18 @@ def test_plot_waterfall(self):
 
     def test_plot_waterfall_missing_column(self):
         df = pandas.DataFrame({"name": ["A"], "delta": [1]})
-        self.assertRaise(lambda: plot_waterfall(df, "missing", "name"), ValueError)
+        with self.assertRaises(ValueError):
+            plot_waterfall(df, "missing", "name")
 
     def test_plot_waterfall_missing_label_column(self):
         df = pandas.DataFrame({"name": ["A"], "delta": [1]})
-        self.assertRaise(lambda: plot_waterfall(df, "delta", "missing"), ValueError)
+        with self.assertRaises(ValueError):
+            plot_waterfall(df, "delta", "missing")
 
     def test_plot_waterfall_bad_colors(self):
         df = pandas.DataFrame({"name": ["A"], "delta": [1]})
-        self.assertRaise(
-            lambda: plot_waterfall(df, "delta", "name", colors=("r",)),
-            ValueError,
-        )
+        with self.assertRaises(ValueError):
+            plot_waterfall(df, "delta", "name", colors=("r",))
 
 
 if __name__ == "__main__":

teachpyx/tools/pandas.py

@@ -77,7 +77,12 @@ def plot_waterfall(
     if len(colors) != 3:
         raise ValueError(f"colors must contain 3 values, not {len(colors)}.")
 
-    values = pandas.to_numeric(data[value_column], errors="raise").astype(float)
+    try:
+        values = pandas.to_numeric(data[value_column], errors="raise").astype(float)
+    except ValueError as exc:
+        raise ValueError(
+            f"Column {value_column!r} cannot be converted to numeric values."
+        ) from exc
     labels = data[label_column] if label_column is not None else data.index
     labels = labels.astype(str)