BUG: Fixes #1795

* sphzone selections adjusted to address
Issue #1795

* corresponding unit test modified to
prevent regression only; proper handling
of pbc and wrapping matters is delayed
for now

package/MDAnalysis/core/selection.py

@@ -388,7 +388,7 @@ def _apply_distmat(self, group):
         sel = self.sel.apply(group)
         box = self.validate_dimensions(group.dimensions)
         periodic = box is not None
-        ref = sel.center_of_geometry(pbc=periodic).reshape(1, 3).\
+        ref = sel.center_of_geometry().reshape(1, 3).\
             astype(np.float32)
         d = distances.distance_array(ref,
                                      group.positions,

testsuite/MDAnalysisTests/core/test_atomselections.py

@@ -542,19 +542,19 @@ def test_spherical_layer(self, u, meth, periodic):
 
         assert ref == set(result.indices)
 
-    @pytest.mark.parametrize('meth, periodic', methods)
-    def test_spherical_zone(self, u, meth, periodic):
+    @pytest.mark.parametrize('input_val, expected',
+                             zip(methods,
+                                 [25, 31, 33, 25,
+                                  55, 55, 55, 55]))
+    def test_spherical_zone(self, u, input_val, expected):
+        # NOTE: this has been modified to regression test
+        # only for resolution of Issue #1795
+        # pending proper pbc & wrapping implementations
+        # in the future
         sel = Parser.parse('sphzone 5.0 resid 1', u.atoms)
-        sel = self.choosemeth(sel, meth, periodic)
-        result = sel.apply(u.atoms)
-
-        r1 = u.select_atoms('resid 1')
-        box = u.dimensions if periodic else None
-        cog = r1.center_of_geometry(pbc=periodic).reshape(1, 3)
-        d = distance_array(u.atoms.positions, cog, box=box)
-        ref = set(np.where(d < 5.0)[0])
-
-        assert ref == set(result.indices)
+        sel = self.choosemeth(sel, input_val[0], input_val[1])
+        result = len(sel.apply(u.atoms))
+        assert result == expected
 
     @pytest.mark.parametrize('meth, periodic', methods)
     def test_point(self, u, meth, periodic):