@@ -42,7 +42,7 @@ def append_visibility(vis: Union[Visibility, BlockVisibility], othervis: Union[V
     assert vis.phasecentre.separation(othervis.phasecentre).value < 1e-15, "Phasecentres differ"
     assert vis.source == othervis.source, "Not the same source"
     if isinstance(vis, BlockVisibility):
-        assert numpy.testing.assert_array_almost_equal_nulp(vis.frequency, othervis.frequency, nulp=12)
+        assert numpy.max(numpy.abs(vis.frequency - othervis.frequency)) < 1e-6
 
     vis.data = numpy.hstack((vis.data, othervis.data))
     return vis
 
@@ -210,7 +210,7 @@ def test_create_vis_iter(self):
         for i, vis in enumerate(vis_iter):
             assert vis.nvis
             if i == 0:
-                fullvis = vis
+                fullvis = copy_visibility(vis)
                 totalnvis = vis.nvis
             else:
                 fullvis = append_visibility(fullvis, vis)