Add regression test for spherical angleEdge in mesh conversion

Add a conversion test that runs `MpasMeshConverter.x` on the low-resolution
QU test mesh, recomputes `angleEdge` in Python from spherical geometry, and
verifies the converted mesh agrees to tight tolerance. This gives us a
lightweight regression test for the polar `angleEdge` fix without introducing
a dedicated C++ unit-test harness.

Author: xylar

conda_package/tests/test_conversion.py

@@ -1,9 +1,11 @@
 #!/usr/bin/env python
 
 import matplotlib
+import numpy as np
 
 from mpas_tools.io import write_netcdf
 from mpas_tools.mesh.conversion import convert, cull, mask
+from mpas_tools.mesh.spherical import recompute_angle_edge
 
 from .util import get_test_data_file
 
@@ -30,5 +32,21 @@ def test_conversion():
     write_netcdf(dsMask, 'antarctic_mask.nc')
 
 
+def test_conversion_angle_edge():
+    ds_mesh = xarray.open_dataset(
+        get_test_data_file('mesh.QU.1920km.151026.nc')
+    )
+    ds_mesh = convert(dsIn=ds_mesh)
+
+    angle_edge_python = recompute_angle_edge(ds_mesh)
+    angle_diff = np.angle(
+        np.exp(1j * (angle_edge_python.values - ds_mesh.angleEdge.values))
+    )
+
+    assert np.all(np.isfinite(angle_diff))
+    assert np.max(np.abs(angle_diff)) < 1.0e-10
+
+
 if __name__ == '__main__':
     test_conversion()
+    test_conversion_angle_edge()