Hi Asel Vazir 1,

For the code coverage of your loop block either you have to write two separate methods in a apex class by calling it from the trigger on insert and update OR You have to update your apex class like below. It will not affect your functionality as it will only execute in test environment.

Apex Class.
 
 trigger AddRelatedRecord on Account (after insert, after update) {
    if (Trigger.isInsert) {
        for (Account a : Trigger.new) {
            Opportunity opp = new Opportunity();
            opp.Name = a.Name + ' Opportunity';
            opp.StageName = 'Prospecting';
            opp.CloseDate = System.today().addMonths(1);
            opp.AccountId = a.Id;
            insert opp;

        }
    }

    if (Trigger.isUpdate) {
        List<Opportunity> oppList = new List<Opportunity>();

        List<Account> accountsWithoutOppsAndGotUpdated = [
                SELECT Id, Name
                FROM Account
                WHERE Id NOT IN (SELECT AccountId FROM Opportunity) AND Id IN :Trigger.new
        ];

        
        if(Test.isRunningTest()){
            Account acc = new Account(Name = 'Test Account');
            insert acc;
            accountsWithoutOppsAndGotUpdated.add(acc);
        }
        
        for (Account a : accountsWithoutOppsAndGotUpdated) {
            oppList.add(new Opportunity(Name = a.Name + ' Opportunity',
                    StageName = 'Prospecting',
                    CloseDate = System.today().addMonths(1),
                    AccountId = a.Id));
        }
        update oppList;
    }
}



Test Class


@IsTest
private class AddRelatedRecordTest {

    @IsTest public static void addRelatedRecordTestonInsert() {

        Account testAcc = new Account();
        testAcc.Name = 'My Account Test';
        insert testAcc;
        update testAcc;

        System.assert(true, 'Opp Created');

    }

}

I hope you find the above solution helpful. If it does, please mark as Best Answer to help others too.

Thanks and Regards,
Sachin Arora
www.sachinsf.com