public class AddPrimaryContact implements queueable{
   public Contact c;
    public string state;
    public AddPrimaryContact( Contact c,String State){
        this.c = c;
        this.state = state;
    }
    public void execute(QueueableContext context){
        List<Account>acc = [select id ,Name ,(select id ,FirstName,LastName from Contacts) From Account where
                             BillingState = :state LIMIT 200];
        List <Contact>conlst = new List<Contact>();
        for(Account account :acc){
            
            Contact cont = c.clone(false,false,false,false);
            cont.AccountId = account.Id;
            conlst.add(cont);
        }
        insert conlst;
    }
}

@isTest
public class AddPrimaryContactTest {
    @isTest static void testMethod1() {
        // setup
        List<Account> testAcctList = new List<Account>();
        for (Integer i = 0; i < 50; i++) {
            testAcctList.add(new Account(BillingState = 'OR', name = 'TestAccount' + i));
        }
        for (Integer j = 0; j < 50; j++) {
            testAcctList.add(new Account(BillingState = 'WA', name = 'TestAccount' + j));
		}
        insert testAcctList;
        
        Contact c = new Contact(FirstName='Test', LastName='test');
        String state = 'OR';
        AddPrimaryContact apc = new AddPrimaryContact(c, state);
        
        // execution
        Test.startTest();
        	System.enqueueJob(apc);
        Test.stopTest();
        
        // result
        System.assertEquals(50, [SELECT count() FROM Contact WHERE accountId IN (SELECT Id FROM Account WHERE BillingState = :state)]);
    }
}