How to write test class for code coverage of pagereference method in Salesforce?

Apex class:

public with sharing class opportunityController{
public Opportunity opp {get;set;}
public opportunityController(){
opp = new Opportunity ();
}

public pageReference save(){
insert opp;
pagereference page =new ApexPages.StandardController(opp).view();//pageReference ('/apex/OpportunityPage');
page.setRedirect(true);
return page;
}
}

Test Class:

@isTest

public class testOpportunityController{
public static testMethod void testOpp () {
opportunityController oppC = new opportunityController ();
pageReference pager = page.OpportunityPage;
Test.setCurrentPage(pager);
oppC.opp.Name = 'abc';
oppC.opp.Stagename = 'Prospecting';
oppC.opp.Closedate = system.today();
oppC.save();
system.assert(oppC.opp.Id != null);

apexPages.Currentpage().getParameters().put('Id',opp.id);
}
}