Trigger updateLZU on Opportunity (before insert, before update) {

	set <string> ZipCodes = new Set <string>( ); 
	//creates a set labeled zip codes to hold the Parcel Zip Codes being referenced 

	for ( opportunity l : trigger.new) {
	
		If ( l.Parcel_Zip__c != null) {
	
			ZipCodes.add (l.Parcel_Zip__c);}
	}
	//loads the Parcel Zip Code field values into the ZipCodes set using a for loop that starts when the Parcel Zip Code contains a value.

	if ( ZipCodes.size( ) > 0 ) {
	
		map <string, Load_u__c> validLZU = new map <string, Load_u__c> ( );
		//creates a map labeled validLZU with a key of string data type and a value in the Load Zone & Utilites object.
		
		for (Load_u__c obj : [SELECT Id, name, Load_Zone__C FROM Load_u__C WHERE name IN : ZipCodes] ) {
		//creates a for loop that queries the Load Zone & Utilities’ object records for the matching  zip code being stored in the ZipCodes set and returns the name and Load Zone fields.

			validLZU.put (obj.name, obj); 
			//loads the name (zip code) returned by the query into the key value of the validLZU map and loads the query as the map’s value.
		}
		
	for ( opportunity l : trigger.new) {

		if ( trigger.isInsert || trigger.oldMap.get(l.Id).ZipCode != l.Parcel_Zip__c && validLZU.containsKey (l.Parcel_Zip__c)) {
		// if the parcel zip code is inserted or if the parcel zip code is different than what it used to be and the map contains a name equal to the parcel zip code than execute:

			l.load_zone_utility_4__C = validLZU.get (l.Parcel_Zip__c).Load_Zone__C;
			//set the Load Zone & Utility field in the opportunity object to the corresponding Load Zone & utility field in the Load Zone & Utility object depending on the parcel zip code.
			
		}

		else if(trigger.oldMap.get(l.iD).Parcel_Zip__c != l.Parcel_Zip__c && !validLZU.containsKey(l.Parcel_Zip__c)) {
		// if the old parcel zip code is equal to the current parcel zip code and the map does not contain the parcel zip code execute:

			l. load_zone_utility_4__C __C = null;
			//set the Load Zone & Utility field in the opportunity object to null.
	}
}
}
}

@isTest
private class opportunityLZUTriggerTestClass {

Static testMethod void validateLZU(){

date myDate = date.newInstance(2016, 2, 17);
account myAccount = new account ();
//create myDate and myAccount variables to be inputted into the newOp opportunity.

opportunity newOp = new opportunity() ;
//create the newOp record in the opportunity object to play as a test record in the opportunity trigger.

newOp.name = ‘Newman Tower’;
newOp.account = myAccount;
newOp.type = 'New Business';
newOp.closeDate = myDate;
newOp.stageName = 'new';
newOp.parcel_zip__c = '02052';
newOp.Load_Zone_Utility_4__c = null;
//add values to the newOp record’s required fields. 
//because Load_Zone_Utility_4__c field is being auto-populated depending on the parcel zip code after the trigger, and is therfore currently blank, set to null.

test.startTest();
//start the test

insert newOp;
//insert the newly created record, newOp, into the opportunity object. 

test.stopTest();
//stop the test

Opportunity opQuery = [SELECT name, Load_Zone_Utility_4__c FROM opportunity WHERE name = ‘Newman Tower’];
//query the records in the opportunity object to return the name and Load Zone & Utility fields from the opportunity object where the name is equal to ‘Newman Tower’.
// set this query to the variable opQuery.

system.assertEquals('NEMA Eversource', opQuery.Load_Zone_Utility_4__c);
// Check that the Load Zone & Utility field in the query opQuery is equal to ‘NEMA Eversource’, which it should as the trigger’s job was to update this field based off of the zip code ‘02052’


}
}