I have written Like this 

@isTest
private class Assert_Creation_TC {
static testMethod void validateabc() {
Branch__c b= new Branch__c();
b.Name='sdf';
b.Branch_Code__c='xc';
b.City__c='df';
b.City__c='ww';
b.Pin_Code__c='wewe';
b.Invoice_Number_Cash__c=23;
b.Invoice_Number_General__c=23;
b.Invoice_Number_Online__c=23;
insert b;

account a= new account();
a.name='dsad';
insert a;
user u = [select id from user limit 1];

//Pricebook2 standardPB = [select id from Pricebook2 limit 1];

Pricebook2 pb = new Pricebook2(Name = 'Standard Price Book 2009', Description = 'Price Book 2009 Products', IsActive = true);
insert pb;
Product2 prod = new Product2(Name = 'Anti-infectives 2007', Family = 'Best Practices', IsActive = true);

PricebookEntry pbe = new PricebookEntry(Pricebook2Id = pb.Id,Product2Id = prod.Id, UnitPrice = 10000, IsActive = true, UseStandardPrice = false);
insert pbe;

opportunity o = new opportunity();
o.Name='ssd';
o.CloseDate=date.ValueOf('2011-09-21');
o.Branch__c=b.id;
o.Manager__c=u.id;
o.Payment_Option__c='Full Payment';
o.StageName='Follow up for Evaluation';
o.Accountid=a.id;

insert o;
update o;

opportunitylineitem op=new opportunitylineitem();
op.Quantity=1;
op.UnitPrice=76;
op.OpportunityId=o.id;
op.PricebookEntryId = pbe.id;
insert op;

asset ass=new asset();
ass.name=o.name;

}
}

Here is the error:

Method NameTotal Time (ms)MessageStack Trace