3.6+ compatible tests rewritten for 3.5.0 compatibility

Mock methods such as Mock.assert_called_once() are new in 3.6.0.
For compatibility with 3.5+ these have been replaced with
e.g. assertEqual( Mock.call_count, 1 )

tests/test_lookup_table.py

@@ -36,7 +36,7 @@ def test_nearest_neighbour_lookup_table_is_initialised( self, mock_generate_near
         self.assertEqual( lookup_table.cn_energy, 'baz' )
         self.assertEqual( lookup_table.connected_site_pairs, 'qux' )
         self.assertEqual( lookup_table.site_specific_coordination_per_site, 'quux' )
-        mock_generate_nearest_neighbour_lookup_table.assert_called_once()
+        self.assertEqual( mock_generate_nearest_neighbour_lookup_table.call_count, 1 )
 
     def test_lookup_table_init_with_invalid_hamiltonian_keywork_raises_ValueError( self ):
         hamiltonian = 'foo'

tests/test_simulation.py

@@ -23,9 +23,9 @@ def test_reset( self ):
         simulation.atoms = Mock( spec=Species )
         simulation.atoms.atoms = [ Mock( spec=Atom ), Mock( spec=Atom ) ]
         simulation.reset()
-        simulation.lattice.reset.assert_called()
-        simulation.atoms.atoms[0].reset.assert_called()
-        simulation.atoms.atoms[1].reset.assert_called()
+        self.assertEqual( simulation.lattice.reset.call_count, 1 )
+        self.assertEqual( simulation.atoms.atoms[0].reset.call_count, 1 )
+        self.assertEqual( simulation.atoms.atoms[1].reset.call_count, 1 )
 
     def test_set_number_of_atoms( self ):
         simulation = Simulation()
@@ -144,7 +144,7 @@ def test_run_with_equilibration_steps( self ):
         simulation.number_of_jumps = 30
         simulation.run()
         self.assertEqual( simulation.lattice.jump.call_count, 20+30 )
-        simulation.reset.assert_called()
+        self.assertEqual( simulation.reset.call_count, 1 )
 
 class SimulationResultsTestCase( unittest.TestCase ):