Write a trigger that creates a related record (e.g., use Account & Contact Objects) after a new record is inserted

trigger AccountTrigger on Account (after insert) {
    if (Trigger.isInsert && Trigger.isAfter) {
        AccountTriggerHandler.createContacts(Trigger.new);
    }
}
  

public class AccountTriggerHandler {
	public static void createContacts(List newAccounts) {
		List contactsToCreate = new List();
		
		for (Account acc : newAccounts) {
			Contact newContact = new Contact(
				FirstName = 'First Name',
				LastName = 'Last Name',
				AccountId = acc.Id
			);
			contactsToCreate.add(newContact);
		}
		
		if (!contactsToCreate.isEmpty()) {
			insert contactsToCreate;
		}
	}
}

@isTest
public class AccountTriggerHandlerTest {
	
	@isTest
	static void testCreateContactAfterAccountInsert() {
		// Test scenario where a single Account is inserted
		
		System.Test.startTest();
		Account acc = new Account(Name = 'Test Account');
		insert acc;
		System.Test.stopTest();
		
		Contact createdContact = [SELECT Id, FirstName, LastName, AccountId FROM Contact WHERE AccountId = :acc.Id LIMIT 1];
		
		// Verify that a Contact was created and is associated with the Account
		System.assertNotEquals(null, createdContact, 'Contact should be created');
		System.assertEquals('First Name', createdContact.FirstName, 'First Name should be default');
		System.assertEquals('Last Name', createdContact.LastName, 'Last Name should be default');
		System.assertEquals(acc.Id, createdContact.AccountId, 'Contact should be related to the Account');
	}

	@isTest
	static void testCreateContactsForMultipleAccounts() {
		// Test scenario where multiple Accounts are inserted
		
		System.Test.startTest();
		List accounts = new List();
		for (Integer i = 0; i < 3; i++) {
			accounts.add(new Account(Name = 'Test Account ' + i));
		}
		insert accounts;
		System.Test.stopTest();

		List createdContacts = [SELECT Id, FirstName, LastName, AccountId FROM Contact WHERE AccountId IN :accounts];
		
		// Verify that a Contact was created for each Account
		System.assertEquals(3, createdContacts.size(), 'There should be 3 Contacts created');

		for (Account acc : accounts) {
			Boolean contactExists = false;
			for (Contact con : createdContacts) {
				if (con.AccountId == acc.Id) {
					contactExists = true;
					break;
				}
			}
			System.assertEquals(true, contactExists, 'A Contact should be created for each Account');
		}
	}
}