Move time dimension to the front in select_and_process_variables method

src/access_moppy/atmosphere.py

@@ -230,6 +230,11 @@ def select_and_process_variables(self):
             if dim not in transpose_order and self.ds[self.cmor_name][dim].size == 1:
                 self.ds[self.cmor_name] = self.ds[self.cmor_name].squeeze(dim)
 
+        if "time" in transpose_order:
+            transpose_order = ["time"] + [
+                dim for dim in transpose_order if dim != "time"
+            ]
+
         self.ds[self.cmor_name] = self.ds[self.cmor_name].transpose(*transpose_order)
 
     def update_attributes(self):

tests/unit/test_sea_ice.py

@@ -0,0 +1,75 @@
+from unittest.mock import Mock, patch
+
+import numpy as np
+import pandas as pd
+import pytest
+import xarray as xr
+
+from access_moppy.sea_ice import SeaIce_CMORiser
+
+
+class TestSeaIceCMORiser:
+    """Unit tests for sea-ice CMORisation."""
+
+    @pytest.fixture
+    def mock_vocab(self):
+        """Mock vocabulary for sea-ice tests."""
+        vocab = Mock()
+        vocab.source_id = "ACCESS-ESM1.6"
+        vocab.variable = {"units": "1", "type": "real"}
+        vocab._get_nominal_resolution = Mock(return_value="1deg")
+        vocab._get_axes = Mock(return_value=({}, {}))
+        vocab._get_required_bounds_variables = Mock(return_value=({}, {}))
+        return vocab
+
+    @pytest.fixture
+    def mock_mapping(self):
+        """Mock variable mapping for sea-ice tests."""
+        return {
+            "siconc": {
+                "model_variables": ["ice_conc"],
+                "calculation": {"type": "direct"},
+            }
+        }
+
+    @pytest.fixture
+    def mock_seaice_dataset(self):
+        """Create a mock sea-ice dataset with time not in first position."""
+        time = pd.date_range("2000-01-01", periods=3, freq="ME")
+        nj = np.arange(2)
+        ni = np.arange(4)
+
+        return xr.Dataset(
+            data_vars={
+                "ice_conc": (
+                    ["nj", "time", "ni"],
+                    np.random.random((2, 3, 4)),
+                    {"coordinates": "ULON ULAT", "units": "1"},
+                )
+            },
+            coords={
+                "time": ("time", time),
+                "nj": ("nj", nj),
+                "ni": ("ni", ni),
+            },
+        )
+
+    @pytest.mark.unit
+    def test_select_and_process_variables_moves_time_to_first_dimension(
+        self, mock_vocab, mock_mapping, mock_seaice_dataset, temp_dir
+    ):
+        """Ensure the processed sea-ice variable has time as the leading dimension."""
+        with patch("access_moppy.sea_ice.Supergrid"):
+            with patch("access_moppy.ocean.CMORiser.load_dataset", return_value=None):
+                cmoriser = SeaIce_CMORiser(
+                    input_paths=["test.nc"],
+                    output_path=str(temp_dir),
+                    compound_name="SImon.siconc",
+                    vocab=mock_vocab,
+                    variable_mapping=mock_mapping,
+                )
+                cmoriser.ds = mock_seaice_dataset
+
+                cmoriser.select_and_process_variables()
+
+                assert cmoriser.ds[cmoriser.cmor_name].dims == ("time", "j", "i")