Accept new copy behaviour from dask/dask#9555.

docs/src/whatsnew/latest.rst

@@ -127,6 +127,16 @@ This document explains the changes made to Iris for this release
    :mod:`iris.palette` in response to a deprecation warning. Using the new
    Matplotlib API also means a ``matplotlib>=3.5`` pin. (:pull:`4998`)
 
+#. `@trexfeathers`_ altered testing to accept new Dask copying behaviour from
+   `dask/dask#9555`_ - copies of a Dask array created using ``da.from_array()``
+   will all ``compute()`` to a shared identical array. So creating a
+   :class:`~iris.cube.Cube` using ``Cube(data=da.from_array(...``, then
+   using :class:`~iris.cube.Cube` :meth:`~iris.cube.Cube.copy`,
+   will produce two :class:`~iris.cube.Cube`\s that both return an identical
+   array when requesting :class:`~iris.cube.Cube` :attr:`~iris.cube.Cube.data`.
+   We do not expect this to affect typical user workflows but please get in
+   touch if you need help. (:pull:`5041`)
+
 
 📚 Documentation
 ================
@@ -180,3 +190,4 @@ This document explains the changes made to Iris for this release
 .. _pypa/setuptools#1684: https://github.com/pypa/setuptools/issues/1684
 .. _SciTools/cartopy@fcb784d: https://github.com/SciTools/cartopy/commit/fcb784daa65d95ed9a74b02ca292801c02bc4108
 .. _SciTools/cartopy@8860a81: https://github.com/SciTools/cartopy/commit/8860a8186d4dc62478e74c83f3b2b3e8f791372e
+.. _dask/dask#9555: https://github.com/dask/dask/pull/9555

lib/iris/tests/unit/cube/test_Cube.py

@@ -1865,12 +1865,14 @@ class Test_copy(tests.IrisTest):
     def _check_copy(self, cube, cube_copy):
         self.assertIsNot(cube_copy, cube)
         self.assertEqual(cube_copy, cube)
-        self.assertIsNot(cube_copy.data, cube.data)
+        self.assertIsNot(cube_copy.core_data(), cube.core_data())
         if ma.isMaskedArray(cube.data):
             self.assertMaskedArrayEqual(cube_copy.data, cube.data)
             if cube.data.mask is not ma.nomask:
                 # "No mask" is a constant : all other cases must be distinct.
-                self.assertIsNot(cube_copy.data.mask, cube.data.mask)
+                self.assertIsNot(
+                    cube_copy.core_data().mask, cube.core_data().mask
+                )
         else:
             self.assertArrayEqual(cube_copy.data, cube.data)
 
@@ -1911,6 +1913,9 @@ def test__masked_scalar_arraymask(self):
         self._check_copy(cube, cube.copy())
 
     def test__lazy(self):
+        # 2022-11-02: Dask's current behaviour is that the computed array will
+        #  be the same for cube and cube.copy(), even if the Dask arrays are
+        #  different.
         cube = Cube(as_lazy_data(np.array([1, 0])))
         self._check_copy(cube, cube.copy())