Update tests following review comments

Author: daflack

Diff for: src/CSET/operators/collapse.py

@@ -234,25 +234,26 @@ def collapse_by_validity_time(
     merged_list_1 = new_cubelist.merge(unique=False)
     # Create a new "fake" coordinate and apply to each remaining cube to allow
     # final merging to take place into a single cube.
-    fake_time = 0
-    for sub_cube in merged_list_1:
-        fake_time_coord = iris.coords.AuxCoord(fake_time)
-        fake_time_coord.units = "1"
-        fake_time_coord.rename("fake_time_coord")
-        sub_cube.add_aux_coord(fake_time_coord)
-        fake_time += 1
+    equalised_validity_time = iris.coords.AuxCoord(
+        points=0, long_name="equalised_validity_time", units="1"
+    )
+    for sub_cube, eq_valid_time in zip(
+        merged_list_1, range(len(merged_list_1)), strict=True
+    ):
+        sub_cube.add_aux_coord(equalised_validity_time.copy(points=eq_valid_time))
+
     # Merge CubeList to create final cube.
     final_cube = merged_list_1.merge_cube()
     # Collapse over fake_time_coord to represent collapsing over validity time.
     if method == "PERCENTILE":
         collapsed_cube = collapse(
             final_cube,
-            "fake_time_coord",
+            "equalised_validity_time",
             method,
             additional_percent=additional_percent,
         )
     else:
-        collapsed_cube = collapse(final_cube, "fake_time_coord", method)
+        collapsed_cube = collapse(final_cube, "equalised_validity_time", method)
     return collapsed_cube
 
 

Diff for: tests/operators/test_collapse.py

@@ -180,23 +180,24 @@ def test_collapse_by_validity_time_cubelist(long_forecast_many_cubes):
 
 def test_collapse_by_validity_time_percentile(long_forecast_multi_day):
     """Reduce by validity time with percentiles."""
-    with pytest.raises(ValueError):
-        collapse.collapse_by_validity_time(long_forecast_multi_day, "PERCENTILE")
     # Test successful collapsing by validity time.
     collapsed_cube = collapse.collapse_by_validity_time(
         long_forecast_multi_day, "PERCENTILE", additional_percent=[25, 75]
     )
-    expected_cube = "<iris 'Cube' of air_temperature / (K) (percentile_over_fake_time_coord: 2; time: 145; grid_latitude: 3; grid_longitude: 3)>"
+    expected_cube = "<iris 'Cube' of air_temperature / (K) (percentile_over_equalised_validity_time: 2; time: 145; grid_latitude: 3; grid_longitude: 3)>"
     assert repr(collapsed_cube) == expected_cube
 
 
+def test_collapse_by_validity_time_percentile_fail(long_forecast_multi_day):
+    """Test not specifying additional percent fails."""
+    with pytest.raises(ValueError):
+        collapse.collapse_by_validity_time(long_forecast_multi_day, "PERCENTILE")
+
+
 def test_collapse_by_validity_time_cubelist_percentile(long_forecast_many_cubes):
     """Convert to cube and reduce by validity time with percentiles."""
-    with pytest.raises(ValueError):
-        collapse.collapse_by_validity_time(long_forecast_many_cubes, "PERCENTILE")
-    # Test successful collapsing by validity time.
     collapsed_cube = collapse.collapse_by_validity_time(
         long_forecast_many_cubes, "PERCENTILE", additional_percent=[25, 75]
     )
-    expected_cube = "<iris 'Cube' of air_temperature / (K) (percentile_over_fake_time_coord: 2; time: 145; grid_latitude: 3; grid_longitude: 3)>"
+    expected_cube = "<iris 'Cube' of air_temperature / (K) (percentile_over_equalised_validity_time: 2; time: 145; grid_latitude: 3; grid_longitude: 3)>"
     assert repr(collapsed_cube) == expected_cube