add test that ensures warning is issued

Author: jgostick

tests/unit/models/geometry/PoreSurfaceAreaTest.py

@@ -2,6 +2,7 @@
 import openpnm.models.geometry.pore_surface_area as mods
 import numpy as np
 from numpy.testing import assert_allclose
+import pytest
 
 
 class PoreSurfaceAreaTest:
@@ -69,6 +70,22 @@ def test_circle_multi_geom(self):
         assert_allclose(a, b)
         assert_allclose(c, d)
 
+    def test_negative_surface_area(self):
+        pn = op.network.Cubic([2, 1, 1])
+        pn.add_model_collection(op.models.collections.geometry.circles_and_rectangles)
+        pn.regenerate_models()
+        pn.add_model(propname='pore.surface_area', model=op.models.geometry.pore_surface_area.circle)
+        pn['throat.cross_sectional_area'] = 100
+        pn.regenerate_models('pore.surface_area@all')
+        assert np.all(pn['pore.surface_area'] == 0)
+        with pytest.warns():
+            pn.add_model(
+                propname='pore.surface_area',
+                model=op.models.geometry.pore_surface_area.circle,
+                amin=None,
+            )
+        assert np.all(pn['pore.surface_area'] < 0)
+
 
 if __name__ == '__main__':