Two cases

Author: scott.robinson

docs/src/whatsnew/latest.rst

@@ -56,6 +56,11 @@ This document explains the changes made to Iris for this release
    cubes with masked :class:`iris.coords.CellMeasure`.
    (:issue:`5147`, :pull:`5181`)
 
+#. `@scottrobinson02`_ fixed :class:`iris.util.new_axis` creating an anonymous new
+   dimension, when the scalar coord provided is already a dim coord.
+   (:issue:`4415`, :pull:`5194`)
+
+
 
 💣 Incompatible Changes
 =======================

lib/iris/tests/unit/util/test_new_axis.py

@@ -122,7 +122,7 @@ def test_existing_dim_coord(self, stock_cube):
         stock_cube.add_aux_coord(coord)
 
         new_cube = iris.util.new_axis(stock_cube, coord)
-        with pytest.raises(iris.exceptions.CoordinateNotFoundError):
+        with pytest.raises(ValueError, match="is already a dimension coordinate."):
             iris.util.new_axis(new_cube, coord)
 
     def test_promote_non_scalar(self, stock_cube):

lib/iris/util.py

@@ -1171,9 +1171,15 @@ def _handle_dimensional_metadata(
         cube_add_method(new_dm_item, new_dims)
 
     if scalar_coord is not None:
-        scalar_coord = src_cube.coord(scalar_coord, dim_coords=False)
+        scalar_coord = src_cube.coord(scalar_coord)
+        try:
+            src_cube.coord(scalar_coord, dim_coords=False)
+        except iris.exceptions.CoordinateNotFoundError:
+            emsg = scalar_coord.name() + " is already a dimension coordinate."
+            raise ValueError(emsg)
+
         if not scalar_coord.shape == (1,):
-            emsg = scalar_coord.name() + "is not a scalar coordinate."
+            emsg = scalar_coord.name() + " is not a scalar coordinate."
             raise ValueError(emsg)
 
     expand_extras = [