Test Class not increasing the code coverage of trigger - unit-testing

Question

I have created a trigger that converts products(Lineitems) to assets when opportunity moves to closed won stage. It is working fine on Sandbox but the problem is code coverage. When I'm writing a test class the method is passed but the code coverage of trigger is still 0%. Any help would be appreciated.
#Trigger
trigger OpportunityTrigger on Opportunity (after insert,after update) {
OpportunityTriggerHandler.testhandler(trigger.new); }
#Class
public Class OpportunityTriggerHandler {
public static Boolean isFirstTime = true;
public static void testhandler(List <Opportunity> oplist)
{
list <OpportunityLineItem> OLI=new list<OpportunityLineItem>();
list<Asset> ast = new list<Asset>();
for(Opportunity o: oplist) {
if(o.isWon == true && o.HasOpportunityLineItem == true && o.AccountId !=null)
{
String opptyId = o.Id;
OLI = [Select UnitPrice, Quantity , PricebookEntry.Product2Id, PricebookEntry.Product2.Name, Description From OpportunityLineItem where OpportunityId = :opptyId ];
Asset a = new Asset();
for(OpportunityLineItem ol: OLI){
List<Asset> ast1 = [Select Product2Id From Asset where Opportunity__c = :opptyId and Product2Id = : ol.PricebookEntry.Product2Id];
if(ast1 .size()>0){
string prdId = string.valueOf(ast1[0].Product2Id );
string oliId = ol.PricebookEntry.Product2Id;
if(prdId != oliId ){
a = new Asset();
a.AccountId = o.AccountId;
a.Product2Id = ol.PricebookEntry.Product2Id;
a.Quantity = ol.Quantity;
a.Price = ol.UnitPrice;
a.PurchaseDate = o.CloseDate;
a.Status = 'Purchased';
a.Description = ol.Description;
a.Name = ol.PricebookEntry.Product2.Name;
a.Opportunity__c = o.Id;
ast.add(a);
}
}
else{
a = new Asset();
a.AccountId = o.AccountId;
a.Product2Id = ol.PricebookEntry.Product2Id;
a.Quantity = ol.Quantity;
a.Price = ol.UnitPrice;
a.PurchaseDate = o.CloseDate;
a.Status = 'Purchased';
a.Description = ol.Description;
a.Name = ol.PricebookEntry.Product2.Name;
a.Opportunity__c = o.Id;
ast.add(a);
}
}
} } update OLI; insert ast; } }
#testClass
#isTest
public class TestOpportunityTrigger{
Static testmethod void TestOpportunityTrigger(){
Test.startTest();
list <Opportunity> Opty =new list<Opportunity>();
OpportunityTriggerHandler.testhandler(Opty);
Opportunity o = new Opportunity();
OpportunityLineItem ol = new OpportunityLineItem();
Asset a = new Asset();
if(o.isWon == true && o.HasOpportunityLineItem == true && o.AccountId !=null)
{
a = new Asset();
a.AccountId = o.AccountId;
a.Product2Id = ol.PricebookEntry.Product2Id;
a.Quantity = ol.Quantity;
a.Price = ol.UnitPrice;
a.PurchaseDate = o.CloseDate;
a.Status = 'Purchased';
a.Description = ol.Description;
a.Name = ol.PricebookEntry.Product2.Name;
a.Opportunity__c = o.Id;
try{ insert a; }
catch(exception e)
{ system.assert(False); }
Test.stopTest();
}
else{}
}}