Test latitude weighting function with specific values

src/scores/functions.py

@@ -30,6 +30,14 @@ def create_latitude_weights(latitudes):
     which is contained in a particular region. This is approximated by the cosine
     of the latitude on an LLXY grid. Nuances not accounted for include the variation in
     latitude across the region, or the irregularity of the surface of the earth.
+
+    Returns:
+        An xarray containing the weight values to be used for area approximation
+
+    Args:
+        An xarray (or castable type) containing latitudes between +90 and -90 degrees
+
+    Note - floating point behaviour can vary between systems, precisions and other factors
     """
     weights = np.cos(np.deg2rad(latitudes))
     return weights

tests/scores/test_weights.py

@@ -61,7 +61,6 @@ def test_weights_latitude():
     """
     Tests the use of latitude weightings, not the correctness
     """
-    # TODO: Write a correctness test for latitude weighting conversions to be specified by hand
 
     lat_weightings_values = scores.functions.create_latitude_weights(OBS_2D.latitude)
 
@@ -70,6 +69,28 @@ def test_weights_latitude():
         weighted = score(FCST_2D, OBS_2D, weights=lat_weightings_values)
         assert unweighted != weighted
 
+    # Latitudes in degrees, tested to 8 decimal places
+    latitude_tests = [
+        (90,    0),
+        (89,    0.017452),
+        (45,    0.707107),
+        (22.5,  0.92388),
+        (0,     1),
+        (-22.5, 0.92388),
+        (-45,   0.707107),
+        (-89,   0.017452),
+        (-90,   0)
+    ]
+    latitudes, expected = zip(*latitude_tests)
+    latitudes = xr.DataArray(list(latitudes))  # Will not work from a tuple
+    expected = xr.DataArray(list(expected))  # Will not work from a tuple
+
+    found = scores.functions.create_latitude_weights(latitudes)
+    decimal_places = 6
+    found = found.round(decimal_places)
+    expected = expected.round(decimal_places)
+    assert found.equals(expected)
+
 
 def test_weights_NaN_matching():
     da = xr.DataArray