tests: update tests for read and write configurations

hnn_core/tests/test_io.py

@@ -197,19 +197,19 @@ def test_cell_response_to_dict(jones_2009_network):
     """ Tests _cell_response_to_dict function """
     net = jones_2009_network
 
-    # No simulation so should have None for cell response
+    # Without simulation there should be an empty dict
     result1 = _cell_response_to_dict(net, write_output=True)
-    assert result1 is None
+    assert result1 == dict()
 
     # Check for cell response dictionary after a simulation
     simulate_dipole(net, tstop=2, n_trials=1, dt=0.5)
     assert net.cell_response is not None
     result2 = _cell_response_to_dict(net, write_output=True)
     assert bool(result2) and isinstance(result2, dict)
 
-    # Check for None if kw supplied
+    # Check for empty dict if kw supplied
     result3 = _cell_response_to_dict(net, write_output=False)
-    assert result3 is None
+    assert result3 == dict()
 
 
 def test_rec_array_to_dict(jones_2009_network):