Revert to calculating the points as the mid-points of the new bounds …

…(as per the existing behaviour). Removing lazy points test since they now just inherit the 'laziness' of the bounds.

docs/iris/src/whatsnew/contributions_2.1/newfeature_2018-May-03_multidim_collapse.txt

@@ -1,5 +1,2 @@
 * The partial collapse of multi-dimensional auxiliary coordinates is now
-  supported. Collapsed bounds span the range of the collapsed dimension(s).
-  *Note* the collapsed points now represent the mean over the collapsed
-  dimensions(s) rather than the mid-point as was previously used (for full
-  collapse).
+  supported. Collapsed bounds span the range of the collapsed dimension(s).

lib/iris/coords.py

@@ -1222,7 +1222,7 @@ def serialize(x):
             # Calculate the bounds and points along the right dims
             bounds = al.stack([item.min(axis=dims_to_collapse),
                                item.max(axis=dims_to_collapse)]).T
-            points = item.mean(axis=dims_to_collapse, dtype=self.dtype)
+            points = al.array(bounds.sum(axis=-1) * 0.5, dtype=self.dtype)
 
             # Create the new collapsed coordinate.
             coord = self.copy(points=points, bounds=bounds)

lib/iris/tests/unit/coords/test_Coord.py

@@ -301,19 +301,6 @@ def test_numeric_nd(self):
                                                                 [4, 10],
                                                                 [5, 11]]))
 
-    def test_lazy_nd_points(self):
-        import dask.array as da
-        self.setupTestArrays((3, 4))
-        coord = AuxCoord(self.pts_lazy)
-
-        collapsed_coord = coord.collapsed()
-
-        self.assertTrue(collapsed_coord.has_lazy_points())
-        self.assertFalse(collapsed_coord.has_lazy_bounds())
-
-        self.assertArrayEqual(collapsed_coord.points, da.array([55]))
-        self.assertArrayEqual(collapsed_coord.bounds, da.array([[0, 110]]))
-
     def test_lazy_nd_bounds(self):
         import dask.array as da