Hi
I'm doing a trigger that is triggered from the Assigned Resource.  The trigger works in the UI, however, I'm having an issue with the Test Code.

I receive an error:
FIELD_CUSTOM_VALIDATION_EXCEPTION, Cannot change status from New to Scheduled: []

Now, if i do the same from the UI, there is no error regarding the status change.  The status change is allowed in the FSL administration.  I can assign using the dispatcher console - all good.  And I can mimic the process i'm using in the test code in the UI (editing the SA directly) with out error.  
Wondering if any one has seen this error before?
Code is included below:

@isTest static void test_AssignedResource_Insert() {
		List<AssignedResource> toInsert = new List<AssignedResource>();

		//retrieve a service resource
		List<ServiceResource> listSR = new List<ServiceResource>([SELECT Id, Name FROM ServiceResource WHERE Name = 'Technician One']);
		ServiceResource sr1 = listSR[0];

		// retrieve the Service Appointment created by test data
		List<WorkOrder> workOrders = new List<WorkOrder>([SELECT Id FROM WorkOrder WHERE Subject ='Test Subject1']);
		List<Id> woIds = new List<Id>();
		for (WorkOrder wo : workOrders ) {
			woIds.add(wo.Id);
		}
		if (woIds.size() > 0 ) {
			List<ServiceAppointment> appts = new List<ServiceAppointment> ();
			appts = [SELECT Id FROM ServiceAppointment WHERE Work_Order__c IN :woIds];
			//for all the appts - should be one - create an assigned resource
			if(appts.size()>0) {
				for( ServiceAppointment sa : appts ) {
					sa.SchedStartTime = datetime.newInstance(2019, 4, 19, 11, 00, 0);
					sa.SchedEndTime = datetime.newInstance(2019, 4, 19, 11, 30, 0);

					AssignedResource ar = new AssignedResource(ServiceAppointmentId=sa.Id,ServiceResourceId=sr1.Id);
					toInsert.add(ar);
				}
				update appts;

				insert toInsert;

				List<ServiceAppointment> assignedSA = new List<ServiceAppointment>([SELECT Id,Technician_Name__c FROM ServiceAppointment WHERE Work_Order__c IN :woIds]);
				System.assertEquals(assignedSA.size(), 1);
				System.assertEquals(assignedSA[0].Technician_Name__c,sr1.Name);

			} else {

			}


		} else {
			//exception
			System.assertNotEquals(woIds.size(), 0);
		}


	}

the error occurs on the insert of the assigned resources

insert toInsert;

IF i change the code such that I manually do the status change in the code example:

sa.SchedStartTime = datetime.newInstance(2019, 4, 19, 11, 00, 0);
sa.SchedEndTime = datetime.newInstance(2019, 4, 19, 11, 30, 0);
sa.Status = 'Scheduled';

the error is returned for the update of the service appointments.

update appts;

Feed back greatly appreciated.

Andrew