Unit Test for Apex Trigger that Concatenates Fields - unit-testing

Question

I am trying to write a test for a before trigger that takes fields from a custom object and concatenates them into a custom Key__c field.
The trigger works in the Sandbox and now I am trying to get it into production. However, whenever I try and do a System.assert/assertEquals after I create a purchase and perform DML, the value of Key__c always returns null. I am aware I can create a flow/process to do this, but I am trying to solve this with code for my own edification. How can I get the fields to concatenate and return properly in the test? (the commented out asserts are what I have tried so far, and have failed when run)
trigger Composite_Key on Purchases__c (before insert, before update) {
if(Trigger.isBefore)
{
for(Purchases__c purchase : trigger.new)
{
String eventName = String.isBlank(purchase.Event_name__c)?'':purchase.Event_name__c+'-';
String section = String.isBlank(purchase.section__c)?'':purchase.section__c+'-';
String row = String.isBlank(purchase.row__c)?'':purchase.row__c+'-';
String seat = String.isBlank(String.valueOf(purchase.seat__c))?'':String.valueOf(purchase.seat__c)+'-';
String numseats = String.isBlank(String.valueOf(purchase.number_of_seats__c))?'':String.valueOf(purchase.number_of_seats__c)+'-';
String adddatetime = String.isBlank(String.valueOf(purchase.add_datetime__c))?'':String.valueOf(purchase.add_datetime__c);
purchase.Key__c = eventName + section + row + seat + numseats + adddatetime;
}
}
}
#isTest
public class CompositeKeyTest {
public static testMethod void testPurchase() {
//create a purchase to fire the trigger
Purchases__c purchase = new Purchases__c(Event_name__c = 'test', section__c='test',row__c='test', seat__c=1.0,number_of_seats__c='test',add_datetime__c='test');
Insert purchase;
//System.assert(purchases__c.Key__c.getDescribe().getName() == 'testesttest1testtest');
//System.assertEquals('testtesttest1.0testtest',purchase.Key__c);
}
static testMethod void testbulkPurchase(){
List<Purchases__c> purchaseList = new List<Purchases__c>();
for(integer i=0 ; i < 10; i++)
{
Purchases__c purchaserec = new Purchases__c(Event_name__c = 'test', section__c='test',row__c='test', seat__c= i+1.0 ,number_of_seats__c='test',add_datetime__c='test');
purchaseList.add(purchaserec);
}
insert purchaseList;
//System.assertEquals('testtesttest5testtest',purchaseList[4].Key__c,'Key is not Valid');
}
}

Answer 1

You need to requery the records after inserting them to get the updated data from the triggers/database