Re-design error msg on how to modify all_arrays

Author: bobleesj

src/diffpy/utils/diffraction_objects.py

@@ -188,8 +188,8 @@ def all_arrays(self):
     @all_arrays.setter
     def all_arrays(self, value):
         raise AttributeError(
-            "Direct modification of 'all_arrays' is not allowed."
-            "Please use 'insert_scattering_quantity' to modify it."
+            "Direct modification of attribute 'all_arrays' is not allowed."
+            "Please use 'insert_scattering_quantity' to modify `all_arrays`."
         )
 
     def set_angles_from_list(self, angles_list):

tests/test_diffraction_objects.py

@@ -369,5 +369,9 @@ def test_all_array_setter():
     actual_do = DiffractionObject()
 
     # Attempt to directly modify the property
-    with pytest.raises(AttributeError, match="Direct modification of 'all_arrays' is not allowed."):
+    with pytest.raises(
+        AttributeError,
+        match="Direct modification of attribute 'all_arrays' is not allowed."
+        "Please use 'insert_scattering_quantity' to modify `all_arrays`.",
+    ):
         actual_do.all_arrays = np.empty((4, 4))