Test that normal DOFArrays for empty boundaries have the same number of groups...

Test that normal DOFArrays for empty boundaries have the same number of groups as the corresponding discretization

test/test_grudge.py

@@ -25,6 +25,7 @@ import numpy.linalg as la
 
 from meshmode import _acf       # noqa: F401
 from meshmode.dof_array import flatten, thaw
+import meshmode.mesh.generation as mgen
 
 from pytools.obj_array import flat_obj_array, make_obj_array
 
@@ -1122,6 +1123,24 @@ def test_map_if(actx_factory):
     bind(discr, sym_if)(actx)
 
 
+def test_empty_boundary(actx_factory):
+    # https://github.com/inducer/grudge/issues/54
+
+    actx = actx_factory()
+
+    dim = 2
+    mesh = mgen.generate_regular_rect_mesh(
+            a=(-0.5,)*dim, b=(0.5,)*dim,
+            n=(8,)*dim, order=4)
+    discr = DGDiscretizationWithBoundaries(actx, mesh, order=4)
+    normal = bind(discr,
+            sym.normal(sym.BTAG_NONE, dim, dim=dim - 1))(actx)
+    from meshmode.dof_array import DOFArray
+    for component in normal:
+        assert isinstance(component, DOFArray)
+        assert len(component) == len(discr.discr_from_dd(sym.BTAG_NONE).groups)
+
+
 # You can test individual routines by typing
 # $ python test_grudge.py 'test_routine()'