@isTest
public class OppNamesTest {
    static testmethod void testclass(){
        
    //insert product
    Product2 prod = new Product2(Name = 'Laptop X200',Family = 'Hardware');
    insert prod;
    
  	 Id pricebookId = Test.getStandardPricebookId();
        
     //create a new Opportunity
	Opportunity opp1 = new  Opportunity();
    opp1.Name = 'Test trigger';
    opp1.CloseDate = Date.today();
    opp1.StageName = 'Sourcing Demand';
    insert opp1;
        
    //create a new Opportunity2
	Opportunity opp2 = new  Opportunity();
    opp2.Name = 'Test trigger1';
    opp2.CloseDate = Date.today();
    opp2.StageName = 'Sourcing Demand';
    insert opp2;
        
    //insert pricebook
    PricebookEntry pbe = new PricebookEntry();
    pbe.Pricebook2Id=pricebookId;
    pbe.Product2Id = prod.Id;
    pbe.isActive=True;
   	pbe.UnitPrice = 0.70;
  	pbe.UseStandardPrice=false;
	 insert pbe;
        

        
        //create OLI
       	OpportunityLineItem opli = new OpportunityLineItem();
    	opli.UnitPrice = 57;
    	opli.Quantity = 1;
    	opli.OpportunityId=opp1.Id;
       // opli.PricebookEntryId= pbe.Id;
    	opli.Product2Id = prod.Id;
       	insert opli;
        
        //create OLI
       	OpportunityLineItem opli1 = new OpportunityLineItem();
    	opli1.UnitPrice = 40;
    	opli1.Quantity = 1;
    	opli1.OpportunityId=opp2.Id;
        opli1.PriceBookEntryId=pbe.Id;
    	opli1.Product2Id = prod.Id;
       	insert opli1;	
        
        map<ID,string> MapofNames = new map<ID,string>();
        Product2 prd = new Product2();
        
        MapofNames.put(opli.OpportunityID,opli.Product2Id);
        MapofNames.put(opli1.OpportunityID,opli1.Product2Id);
        
        string namesofOpp1 = [select name from opportunity where Id IN: MapofNames.keySet()].name;
        prd = [select Id,Opportunity_Names__c from Product2 where Id in: MapofNames.values()];
        string allnames=(string) prd.get('Opportunity_Names__c');
        
        prd.Opportunity_Names__c = allnames+';'+namesofOpp1;// concanated the names previous and current
        update prd;
        
        System.assertEquals('Test trigger;Test trigger1', prd.Opportunity_Names__c);
    }
}