My test class showing 0% code coverage in Salesforce?

I have to make trigger on opportunity whenever new opp is created create a post on account.

my trigger

trigger postOnAcc on Opportunity (after insert) {
List<FeedItem> posts = new List<FeedItem>(); //create a list to hold post
List<Id> oppList=new List<Id>(); //create a list to hold new opportunity
for(Opportunity o:Trigger.new) //Iterate for loop on new opportunity
{
oppList.add(o.AccountId); //add opportunity account id in opportunity list
}
for(Opportunity opp: [Select id,name ,AccountId from Opportunity where AccountId in:oppList]) //
{

if(opp.AccountId != null){

FeedItem post = new FeedItem();
Post.ParentId = opp.AccountId;
post.body = 'New Opportunity is created with Opportunity Id - '+opp.Id + ' and Opportunity name is equal to - '+opp.Name;
posts.add(post); //add this post in posts List

}
}
insert posts;
}

my test class

@istest
private class testclass {
static testmethod void testclass()
{
Account a=new Account();
a.Name='AK';
insert a;

Opportunity o=new opportunity();
o.Name='AJ';
o.AccountId=a.Id;
insert o;

FeedItem post = new FeedItem();
Post.ParentId = o.AccountId;
post.body = 'New Opportunity is created with Opportunity Id - '+o.Id + ' and Opportunity name is equal to - '+o.Name;
insert post;

}
}