fix utilisation bug, write test

Author: geraintpalmer

ciw/node.py

@@ -444,7 +444,7 @@ def wrap_up_servers(self, current_time):
             for srvr in self.servers:
                 srvr.total_time = self.increment_time(current_time, -srvr.start_date)
                 if srvr.busy:
-                    srvr.busy_time += self.increment_time(current_time, -srvr.cust.arrival_date)
+                    srvr.busy_time += self.increment_time(current_time, -srvr.cust.service_start_date)
 
 
     def write_individual_record(self, individual):

ciw/tests/test_node.py

@@ -637,6 +637,18 @@ def test_server_utilisation_with_schedules(self):
         recs = Q.get_all_records()
         self.assertEqual(Q.transitive_nodes[0].server_utilisation, 21.0/37.0)
 
+    def test_server_utilisation_with_wrapup(self):
+        N = ciw.create_network(
+            Arrival_distributions=[['Exponential',7.14]],
+            Service_distributions=[['Exponential',0.04]],
+            Number_of_servers=[70]
+        )
+        ciw.seed(1)
+        Q = ciw.Simulation(N)
+        Q.simulate_until_max_time(168)
+        for srvr in Q.transitive_nodes[0].servers:
+            self.assertGreaterEqual(srvr.total_time, srvr.busy_time)
+
     def test_num_inds_equal_len_all_inds(self):
         # Create a Simulatin class that inherits form ciw.Simulation so that
         # an assertion than number_of_individuals == len(all_individuals)