Can't deploy Trigger I wrote to update Opportunity from changes to Account Field - Apex Novice

Question

Wrote an apex trigger to update associated opportunities when a specific field is updated (which reflects the account's signup stage in our backend).

trigger updateopportunity on Account (after update) {
    
    set<Id> accountIds = new set<Id>();
    for (Account acc : Trigger.new)
    {
        Account old = Trigger.oldMap.get(acc.Id);
        if (acc.CD_Status__c=='pending' && acc.CD_Status__c != old.CD_Status__c) 
        {
        accountIds.add(acc.Id);
        }
    }
    if (!accountIds.isEmpty()) {
        List <Opportunity> opps = [
            select Id, StageName
            From Opportunity
            where AccountId in: accountIds
            and RecordTypeId ='0128d000000pBdUAAU'
            and StageName != 'Started SignUp'
            ];
        if (!opps.isEmpty()) {
                for (Opportunity opp : opps) {
                opp.StageName = 'Started SignUp';
            }
            update opps;
        }
    }
}

Read that to deploy in production, I needed to run Apex Class Tests? from the developer console. Not sure how exactly I am meant to format this. the best I could come up wiht, but to no success, was below.

Basically tried creating both an Account and related Opportunity, and then updating said Account's CD_Status__c to 'pending' (the requirement for the trigger), but not entirely sure how to go about initiating the test. I keep getting errors

@isTest
public class updateopportunity {
    @isTest static void Testupdateopportunity() {
        // set up user
        User u1 = [select id from User WHERE email='[email protected]'];
        
        //Run as u1
        System.RunAs(u1)
        
        //New Account Record
        Account acc = new Account();
        acc.Name = 'Test Account';
        acc.industry = 'Test';
        acc.BillingCountry = 'GB';
        acc.Account_Stage__c='Demo Booked';
        acc.Website='test.com';
        acc.Type='Prospect';
        insert acc;
        
        //New Opportunity
        Opportunity opp = new Opportunity();
        opp.Name = 'Test Opp';
        opp.CloseDate = system.today().addDays(7);
        opp.StageName = 'Demo Completed';
        opp.Type = 'New Business';
        opp.RecordTypeId = '0128d000000pBdUAAU';
        opp.AccountId = acc.Id;
        opp.demobookedby__c='Rod';
        opp.datedemobooked__c=system.today();
        insert opp;
        
        //Update Account Field
        acc.CD_Status__c='pending';
        acc.Account_Stage__c='Started SignUp';
        updated.acc;
        
        test.stopTest()
        
        //check result of test - but not too sure how to go about this or if this is the correct format at all
        Select opp.StageName WHERE opp.AccountId=acc.Id
       
    }
}

Answer 1

sfdcfox is correct, as always.

But I wanted to also recommend taking some time to learn best practices. Your triggers should contain 0 business logic. But instead make a call to your Account Trigger Handler that knows what needs to be done in the After Update context. Hard coded record Ids are also a major no no. You could replace that with custom meta data etc..