Salesforce trailhead - Asynchronous Apex Controlling Processes with Queueable Apex

AddPrimaryContact.cls

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 qc) {
        system.debug('this.c = '+this.c+' this.state = '+this.state);
        List<Account> acc_lst = new List<account>([select id, name, BillingState from account where account.BillingState = :this.state limit 200]);
        List<contact> c_lst = new List<contact>();
        for(account a: acc_lst) {
            contact c = new contact();
            c = this.c.clone(false, false, false, false);
            c.AccountId = a.Id;
            c_lst.add(c);
        }
        insert c_lst;
    }

}

AddPrimaryContactTest.cls

@IsTest
public class AddPrimaryContactTest {
    
    @IsTest
    public static void testing() {
        List<account> acc_lst = new List<account>();
        for (Integer i=0; i<50;i++) {
            account a = new account(name=string.valueOf(i),billingstate='NY');
            system.debug('account a = '+a);
            acc_lst.add(a);
        }
        for (Integer i=0; i<50;i++) {
            account a = new account(name=string.valueOf(50+i),billingstate='CA');
            system.debug('account a = '+a);
            acc_lst.add(a);
        }      
        insert acc_lst;
        Test.startTest();
        contact c = new contact(lastname='alex');
        AddPrimaryContact apc = new AddPrimaryContact(c,'CA');
        system.debug('apc = '+apc);
        System.enqueueJob(apc);
        Test.stopTest();
        List<contact> c_lst = new List<contact>([select id from contact]);
        Integer size = c_lst.size();
        system.assertEquals(50, size);
    }

}

(System Code)
Class.AccountProcessorTest.TestAccountProcessorTest: line 36, column 1
Class.AddPrimaryContactTest.testing: line 17, column 1
i am getting this error