Add extra validation tests for waterfall helper

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

@@ -32,6 +32,17 @@ def test_plot_waterfall_missing_column(self):
         df = pandas.DataFrame({"name": ["A"], "delta": [1]})
         self.assertRaise(lambda: plot_waterfall(df, "missing", "name"), ValueError)
 
+    def test_plot_waterfall_missing_label_column(self):
+        df = pandas.DataFrame({"name": ["A"], "delta": [1]})
+        self.assertRaise(lambda: plot_waterfall(df, "delta", "missing"), ValueError)
+
+    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,
+        )
+
 
 if __name__ == "__main__":
     unittest.main()