I have a simple rigger that automatically creates a custom PO_Number__c record when an Opportunity is created. This PO_Number__c an Account__c lookup field and an Opportunity__c lookup field that also gets automatically populated by the trigger.

In my test class, my first test method singleOpp() succeeds, but I want to test a situation where a builk insert of Opportunities happens. My second test method is bulkOpps(). I'm not sure how to finish this method off to make sure that all the PO_Number__c records that were automatically created have the correct Account__c and Opportunity__c fields.

Any help would be greatly appreciated! Here's my code:

TRIGGER:
 

trigger createPurchaseOrder on Opportunity (after insert) {
    // Initialize PO Numbers to insert list
    List<PO_Number__c> ponsToInsertList = new List<PO_Number__c>();

    for (Opportunity opp : Trigger.new) {
        if (opp.Id != null && AccountId != null) {
            // Create PO Number records
            PO_Number__c pon   = new PO_Number__c();
            pon.Account__c     = opp.AccountId;
            pon.Opportunity__c = opp.Id;
            ponsToInsertList.add(pon);
        }
        if (!ponsToInsertList.isEmpty()) {
            // Insert PO Number records 
            insert ponsToInsertList;
        }
    }
}

@isTest
private class CreatePurchaseOrderTest {
    @isTest static void singleOpp() {
        // Create Account
        Account acc = new Account();
        acc.Name    = 'Test Account';
        insert acc;

        // Create Opportunity
        Opportunity opp = new Opportunity();
        opp.Name        = 'Test Opp';
        opp.CloseDate   = Date.today();
        opp.StageName   = 'Initial Contact';
        opp.AccountId   = acc.Id;
        insert opp;

        // get opp
        List<Opportunity> updatedOpp = [
            SELECT Id, AccountId
              FROM Opportunity
             WHERE Id = :opp.Id
             LIMIT 1
        ];

        // check for PO Number record
        List<PO_Number__c> pon = [
            SELECT Id, Opportunity__c, Account__c
              FROM PO_Number__c
             LIMIT 1
        ];

        System.assertEquals(1, pon.size(), 'pon list size not correct');
        System.assertEquals(updatedOpp.get(0).Id, pon.get(0).Opportunity__c, 'Opportunity on PO Number not correct');
        System.assertEquals(updatedOpp.get(0).AccountId, pon.get(0).Account__c, 'Account on PO Number not correct');
    }

    @isTest static void bulkOpps() {
        // Create multiple Accounts
        List<Account> accList = new List<Account>();
        for (Integer i = 0; i < 500; i++) {
        Account myAcc = new Account();
        myAcc.Name    = 'Test Acc ' + i;
        accList.add(myAcc);
        }
        insert accList;

        // Create multiple Opps
        List<Opportunity> oppList = new List<Opportunity>();
        for (Integer i = 0; i < 500; i++) {
        Opportunity myOpp = new Opportunity();
        myOpp.Name        = 'Test Opp ' + i;
        myOpp.StageName   = 'Initial Contact';
        myOpp.CloseDate   = Date.today();
        myOpp.AccountId   = accList.get(i).Id;
        oppList.add(myOpp);
        }
        insert oppList;

        // Check for PO Number records
        List<PO_Number__c> ponList = [
            SELECT Id, Account__c, Opportunity__c
              FROM PO_Number__c
        ];

        // HOW CAN I DETERMINE IF EACH PO NUMBER HAS THE CORRECT OPPORTUNITY AND ACCOUNT ?????
        // EX: PO Number 1 has Account 1 and Opportunity 1 on it's Account__c and Opportunity__c fields
        // EX: PO Number 1 had Account 2 and Opportunity 2 on it's Account__c and Opportunity__c fields

        System.assertEquals(accList.get(0).Id, ponList.get(0).Account__c, 'Account not correct on PO Number');
        System.assertEquals(oppList.get(0).Id, ponList.get(0).Opportunity__c, 'Opportunity not correct on PO Number');
    }
}