From c994b5b734e05202198d5abff265a5242acff3fc Mon Sep 17 00:00:00 2001
From: Zebedee Nicholls <zebedee.nicholls@climate-energy-college.org>
Date: Mon, 17 Sep 2018 12:27:44 +0200
Subject: [PATCH] Add a test

---
 lib/iris/cube.py                      | 11 ++++++++---
 lib/iris/tests/unit/cube/test_Cube.py | 19 +++++++++++++++++++
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/lib/iris/cube.py b/lib/iris/cube.py
index bd9475b221..562e6ef693 100644
--- a/lib/iris/cube.py
+++ b/lib/iris/cube.py
@@ -3210,8 +3210,13 @@ def collapsed(self, coords, aggregator, **kwargs):
 
         if (isinstance(aggregator, iris.analysis.WeightedAggregator) and
                 not aggregator.uses_weighting(**kwargs)):
-
-            if "cell_area" in [c.standard_name for c in self.cell_measures()]:
+            cell_area = [
+                c for c in self.cell_measures()
+                if c.measure == 'area'
+            ]
+            assert len(cell_area) < 2, "more than one cell area measure"
+            cell_area = cell_area[0] if cell_area else None
+            if cell_area is not None:
                 lon, lat = iris.analysis.cartography._get_lon_lat_coords(self)
 
                 # would be ideal to resuse the below from
@@ -3227,7 +3232,7 @@ def collapsed(self, coords, aggregator, **kwargs):
                 lon_dim = self.coord_dims(lon)
                 lon_dim = lon_dim[0] if lon_dim else None
 
-                ll_weights = self.cell_measure('cell_area').data
+                ll_weights = cell_area.data
 
                 # Now we create an array of weights for each cell. This
                 # process will handle adding the required extra dimensions and
diff --git a/lib/iris/tests/unit/cube/test_Cube.py b/lib/iris/tests/unit/cube/test_Cube.py
index ae0a1abe3b..f78f4493cb 100644
--- a/lib/iris/tests/unit/cube/test_Cube.py
+++ b/lib/iris/tests/unit/cube/test_Cube.py
@@ -393,6 +393,25 @@ def test_lat_lon_weighted_aggregator_alt(self):
         coords = [coord for coord in coords if 'latitude' in coord]
         self._assert_warn_collapse_without_weight(coords, warn)
 
+    def test_lat_lon_cell_area_no_weights(self):
+        # Collapse grid_latitude coordinate with weighted aggregator without
+        # providing weights.  Tests coordinate matching logic.
+        cell_areas = CellMeasure(data=np.arange(4).reshape(2, 2),
+                                 long_name='area',
+                                 measure='area')
+
+        self.cube.add_cell_measure(cell_areas, [0, 1],)
+        self.cube.remove_coord('grid_latitude')
+        self.cube.remove_coord('grid_longitude')
+
+        coords = ['latitude', 'longitude']
+
+        with mock.patch('warnings.warn') as warn:
+            self.cube.collapsed(coords, iris.analysis.MEAN)
+
+        coords = [coord for coord in coords if 'latitude' in coord]
+        self._assert_nowarn_collapse_without_weight(coords, warn)
+
     def test_no_lat_weighted_aggregator_mixed(self):
         # Collapse grid_latitude and an unmatched coordinate (not lat/lon)
         # with weighted aggregator without providing weights.