I'm stumped!

The scenario: 

• Object "ZenDesk Ticket" record is created, with a lookup field to an account, and another lookup field to a contact. 
• The contact record didn't exist until the ZenDesk connector created the ticket record in SF, at which point it also creates the contact
  
• ZenDesk should create the contact with the ticket's related Account also being the contact's related account. Instead, the contact is created as an orphan.
• Not sure if this is relevant, bu the ZenDesk objects/fields/etc are part of a managed package on our org. 

Trigger goal:

• Upon creation of ticket and contact, to identify the account related to the ticket, and update the related contact to also relate to this account. 

Method from my test class:

static testmethod void contact_with_no_account(){
    	
    Account testAccount1 = new Account(Name = 'test account',
                                       	  Type = 'Customer',
                                          Country__c = 'Albania');
        
    insert testAccount1;
                                          
    Contact testContact1 = new Contact(FirstName = 'Test',
                                           LastName = 'Contact',                                          
                                       	   City__c = 'Test city');
        
    insert testContact1;
        
    test.startTest();    
    Zendesk__Zendesk_Ticket__c testTicket1 = new Zendesk__Zendesk_Ticket__c(Zendesk__Organization__c = testAccount1.ID,
                                                                            	Zendesk__Requester__c = testContact1.ID);
    insert testTicket1;
    test.stopTest();
     
    System.assertEquals(testContact1.AccountId, testAccount1.ID);
}

Pretty basic - I make an account, an orphaned contact, and a ticket that relates to both of them, and insert them all. That should set off this trigger: 

(partial) Trigger code: 

trigger Zendesk_Ticket_Trigger on Zendesk__Zendesk_Ticket__c (after insert) {

    
    for (Zendesk__Zendesk_Ticket__c ticket1: [SELECT Id, Zendesk__Organization__c, Zendesk__Requester__r.AccountID FROM Zendesk__Zendesk_Ticket__c WHERE Id IN :Trigger.new
                                             AND Zendesk__Requester__r.AccountID = NULL]){
                                                                                         
        ticket1.Zendesk__Requester__r.AccountID = ticket1.Zendesk__Organization__c;                                                                                                 
        update ticket1.Zendesk__Requester__r;                                                                                               
    }

I wonder if my SOQL query is causing the problem by selecting only the tickets whose related Contact's account ID is NULL - can I fairly assume that to be true when a contact is inserted without an account specified?

The problem:

My system.assertEquals statement is returning the error, because the "requester" contact's account ID is null. Clearly it isn't updating after being assigned ticket1.Organization__c's ID.