Here is my trigger to add a opportunity line item in the oppty.

Set<id> oId = new set<id>();
    for(Opportunity opp : trigger.new){
        oId.add(opp.Id);
    }
    
    Opportunity opp = [select Id ,NRR_value__c ,CurrencyIsoCode,RecordTypeId,recordtype.name from Opportunity where ID =: oId];
    system.debug('opp************'+opp);
     
    PriceBookEntry p = [SELECT Id, Product2Id, Product2.Id, Product2.Name, CurrencyIsoCode FROM PriceBookEntry WHERE 
                        Product2Id='01t3O000003UXKsQAO' and CurrencyIsoCode =: opp.CurrencyIsoCode and Pricebook2Id = '01s0J000002SCKDQA4'];
    system.debug('p***************'+p);
    
    string recordtypename = Schema.SObjectType.Opportunity.getRecordTypeInfosById().get(opp.recordtypeid).getname();
    system.debug(' recordtypename*************'+recordtypename);
    
    List<OpportunityLineItem> oliList = new List<OpportunityLineItem>();
    for(Opportunity op : trigger.new){
        if(opp.RecordType.Name == 'Services Record Type'){
             OpportunityLineItem oli = new OpportunityLineItem();
             oli.OpportunityId = opp.Id;
             oli.Quantity = 1;
             oli.PricebookEntryId = p.Id;
             //oli.name = opp.name;
             
             oli.UnitPrice = opp.NRR_value__c;
             oliList.add(oli);
            system.debug('oliList------------'+oliList);
        }   
     }
     insert oliList;



Test class for this trigger:



@isTest(SeeAllData=true)
public class insertopplineitemTest{
    static testMethod void insertopptylineitemTest() {
        Account acct = new Account(Name = 'Celigo testing account',Billingcountry = 'United States');
        insert acct;
       
        //PriceBook Standard
        PriceBook2 stdPBook = [ SELECT Id, IsActive FROM PriceBook2 WHERE IsStandard = True AND IsActive = TRUE LIMIT 1 ];
       
        //Pricebook Custom
        PriceBook2 custPBook = new PriceBook2( Name = 'Test Pricebook',Description = 'Custom Pricebook',CurrencyIsoCode = 'USD',IsActive = TRUE );
        insert custPBook;
       
        //Product
        Product2 prod = new Product2( Name = 'Celigo Test Product',CurrencyIsoCode = 'USD',isActive = TRUE );
        insert prod;
       
        //PriceBookEntry Standard
        PricebookEntry pbEntry1 = new PricebookEntry( Pricebook2Id = stdPBook.Id,Product2Id = prod.id,CurrencyIsoCode = 'USD',IsActive = TRUE );
        pbEntry1.UnitPrice = 100.0;
        pbEntry1.UseStandardPrice = FALSE;
        insert pbEntry1;
           
        PricebookEntry pbEntry2 = new PricebookEntry( Pricebook2Id = custPBook.Id,Product2Id = prod.id,CurrencyIsoCode = 'USD',IsActive = TRUE );
        pbEntry2.UnitPrice = 200.0;
        pbEntry2.UseStandardPrice = FALSE;
        insert pbEntry2;
       
        
        // Opportunity
        Opportunity oppy = new Opportunity( Name = 'Celigo Test Opportunity',AccountId = acct.Id,CurrencyIsoCode = 'USD',NRR_value__c=100);
        
        //oppy.RecordTypeId=Schema.SObjectType.Opportunity.getRecordTypeInfosByDeveloperName().get('Services_Record_Type').getRecordTypeId();
        oppy.StageName = '0 - Meeting';
        oppy.CloseDate = System.Today()+10;
     
        insert oppy;
           
        // OpportunityLineItem
        OpportunityLineItem opItem1 = new OpportunityLineItem(OpportunityId = oppy.Id, PricebookEntryId = pbEntry1.id);
        opItem1.UnitPrice = 100;
        opItem1.Quantity = 10;
        
        
        insert opItem1;
      
      Test class is passing but I am not able to get code coverage more than 75%. Whatelse we can add in the test class to get more code coverage?