PBECreationWithStandardPrice

//product1
Product2 p = new Product2();
p.Name = 'Test Product';
p.Description = 'Test desc';
p.IsActive = true;
insert p;                                    

//standard price book entry for Product p
PricebookEntry pbe1 = new PricebookEntry();
pbe1.Pricebook2Id = Test.getStandardPricebookId();
pbe1.IsActive = true;
pbe1.Product2Id = p.Id;
pbe1.UseStandardPrice = false;
pbe1.CurrencyISOCode = 'SGD';
pbe1.UnitPrice = 100;                                                       
insert pbe1;                      

//custom pricebook
PriceBook2 pb = new PriceBook2();
pb.Name = 'Custom PB';
pb.IsActive = true;            
insert pb;           

//custom pricebook entry for p1
PricebookEntry pbe = new PricebookEntry();
pbe.Pricebook2Id = pb.Id;
pbe.IsActive = true;
pbe.Product2Id = p.Id;
pbe.UseStandardPrice = false;
pbe.CurrencyISOCode = 'SGD';
pbe.UnitPrice = 100;                                                       
insert pbe; 

//update Pricebookentry to use Standard Price
pbe.UseStandardPrice = true;
update pbe;