add test

Author: siliataider

bindings/pyroot/pythonizations/test/numbadeclare.py

@@ -683,6 +683,17 @@ def square_std_arr(v):
         results = df.Take["RVec<int>"]("square_std_arr").GetValue()[0]
         self.assertTrue(np.array_equal(results, np.array([1, 4, 9])))
 
+    def test_missing_signature_raises(self):
+        """
+        Ensure a RuntimeError is raised when return type cannot be inferred
+        and no explicit signature is provided in the decorator.
+        """
+        def f(x):
+            return x.M()
+
+        with self.assertRaises(Exception):
+            ROOT.RDataFrame(4).Define("v", "ROOT::Math::PtEtaPhiMVector(1, 2, 3, 4)").Define("m", f, ["v"])
+
 
 if __name__ == "__main__":
     unittest.main()