Improve tests, and test for lazy merge result.

Author: pp-mo

lib/iris/tests/integration/merge/test_dataless.py

@@ -4,17 +4,19 @@
 # See LICENSE in the root of the repository for full licensing details.
 """Integration tests for merging with dataless cubes."""
 
+import dask.array as da
 import numpy as np
 
 from iris.coords import AuxCoord, DimCoord
 from iris.cube import Cube, CubeList
 
 
 class TestMergeDataless:
-    def _testcube(self, z=1, name="this", dataless=False):
+    def _testcube(self, z=1, name="this", dataless=False, lazy=False):
         # Create a testcube with a scalar Z coord, for merge testing.
+        data = da.arange(3) if lazy else np.arange(3)
         cube = Cube(
-            [1, 2, 3],
+            data,
             long_name=name,
             dim_coords_and_dims=[(DimCoord([0.0, 1.0, 2], long_name="x"), 0)],
             aux_coords_and_dims=[(AuxCoord([z], long_name="z"), ())],
@@ -25,41 +27,39 @@ def _testcube(self, z=1, name="this", dataless=False):
 
     def test_mixed_passthrough(self):
         # Check that normal merge can handle dataless alongside dataful cubes.
-        cubes = CubeList(
-            [
-                self._testcube(name="this", dataless=False),
-                self._testcube(name="that", dataless=True),
-            ]
-        )
+        cube_normal = self._testcube(name="this", dataless=False)
+        cube_dataless = self._testcube(name="that", dataless=True)
+        cubes = CubeList([cube_normal, cube_dataless])
+
         result = cubes.merge()
+
         assert len(result) == 2
         cube1, cube2 = [result.extract_cube(name) for name in ("this", "that")]
         assert not cube1.is_dataless()
         assert cube2.is_dataless()
 
     def test_dataless_merge(self):
         # Check that dataless cubes can be merged.
-        cubes = CubeList(
-            [
-                self._testcube(z=1, dataless=True),
-                self._testcube(z=2, dataless=True),
-            ]
-        )
+        cube_1 = self._testcube(z=1, dataless=True)
+        cube_2 = self._testcube(z=2, dataless=True)
+        cubes = CubeList([cube_1, cube_2])
+
         cube = cubes.merge_cube()
+
         assert cube.is_dataless()
         assert np.all(cube.coord("z").points == [1, 2])
 
     def test_dataless_dataful_merge(self):
         # Check that dataless cubes can merge **with** regular ones.
-        # Check that dataless cubes can be merged correctly.
-        cubes = CubeList(
-            [
-                self._testcube(z=1, dataless=False),
-                self._testcube(z=2, dataless=True),
-            ]
-        )
+        # Include checking that laziness is preserved.
+        cube_normal = self._testcube(z=1, dataless=False, lazy=True)
+        cube_dataless = self._testcube(z=2, dataless=True)
+        cubes = CubeList([cube_normal, cube_dataless])
+
         cube = cubes.merge_cube()
+
         assert not cube.is_dataless()
+        assert cube.has_lazy_data()
         data_z1, data_z2 = cube[0].data, cube[1].data
-        assert np.all(data_z1 == [1, 2, 3])
+        assert np.all(data_z1 == [0, 1, 2])
         assert np.all(np.ma.getmaskarray(data_z2) == True)  # noqa: E712