hi i have written a controller which populates the data when it loads the page in a editable mode and when the user edits the felds and click on save the data stored in custom object.I am trying to know how can we assign test data to this controller since it is retrieved from another page. cna anybody help me in writing a test class for this scenario.

global with sharing class preferenc 
{

    public PageReference cancel() {
        PageReference p = Page.user_preference;
         p.setRedirect(true);
          return p;
    }


    

 public string guestid;
    public guestuser__c gus{get;set;}

    public preferenc() 
    {
    this.guestid=ApexPages.currentPage().getParameters().get('paramID');   
        if(guestid!=null||guestid!='')
        {
            getdetails(guestid); 
        }   

    }

    
    
    public void getdetails(string guestid)
    {
        List<guestuser__c> guests=[select id,Email__c,Phone__c,Title__c,Email_Optout__c,A_H_interests__c,After_Markets_interests__c,Construction_interests__c,D_O_interests__c,Energy_interests__c,Environmental_interests__c,Financial_Enterprises_interests__c,Healthcare_interests__c,Manufacturing_interests__c,Property_interests__c,RealEstate_interests__c,Technology_interests__c,Windstorm_notification_interests__c from guestuser__c where id=:guestid];
        if(guests.size()>0)
        {
            gus=guests[0];
        }
        else
        {
            
        }
    }
    public PageReference save()
    {
        
          update gus;
          PageReference t = Page.thanks;
          t.setRedirect(true);
          return t;  
    } 
    
    static testMethod void testpreferenc()
    {
      
     
      preferenc controller = new preferenc();
     
      controller.save();    
      controller.cancel();
    }
    
}