diff --git a/python/tests/test_grid_filters.py b/python/tests/test_grid_filters.py
index c8442eee4..fdddaf3a1 100644
--- a/python/tests/test_grid_filters.py
+++ b/python/tests/test_grid_filters.py
@@ -30,18 +30,36 @@ class TestGridFilters:
          grid   = np.random.randint(8,32,(3))
          size   = np.random.random(3)
          origin = np.random.random(3)
-        
          coord0 = eval('grid_filters.{}_coord0(grid,size,origin)'.format(mode))                     # noqa
          _grid,_size,_origin = eval('grid_filters.{}_coord0_2_DNA(coord0.reshape((-1,3)))'.format(mode))
          assert np.allclose(grid,_grid) and np.allclose(size,_size) and np.allclose(origin,_origin)
 
     def test_displacement_fluct_equivalence(self):
+         """Ensure that fluctuations are periodic."""
          size = np.random.random(3)
          grid = np.random.randint(8,32,(3))
          F    = np.random.random(tuple(grid)+(3,3))
          assert np.allclose(grid_filters.node_displacement_fluct(size,F),
                             grid_filters.cell_2_node(grid_filters.cell_displacement_fluct(size,F)))
 
+    def test_interpolation_nonperiodic(self):
+         size = np.random.random(3)
+         grid = np.random.randint(8,32,(3))
+         F    = np.random.random(tuple(grid)+(3,3))
+         assert np.allclose(grid_filters.node_coord(size,F) [1:-1,1:-1,1:-1],grid_filters.cell_2_node(
+                            grid_filters.cell_coord(size,F))[1:-1,1:-1,1:-1])
+
+    @pytest.mark.parametrize('mode',[('cell'),('node')])
+    def test_coord0_origin(self,mode):
+         origin= np.random.random(3)
+         size  = np.random.random(3)                                                                # noqa
+         grid  = np.random.randint(8,32,(3))
+         shifted   = eval('grid_filters.{}_coord0(grid,size,origin)'.format(mode))
+         unshifted = eval('grid_filters.{}_coord0(grid,size)'.format(mode))
+         if   mode == 'cell':
+            assert  np.allclose(shifted,unshifted+np.broadcast_to(origin,tuple(grid[::-1])  +(3,)))
+         elif mode == 'node':
+            assert  np.allclose(shifted,unshifted+np.broadcast_to(origin,tuple(grid[::-1]+1)+(3,)))
 
     @pytest.mark.parametrize('mode',[('cell'),('node')])
     def test_displacement_avg_vanishes(self,mode):