PageReference and ApexPages

PageReference

ApexPages

PageReference page = Page.Mypage;            
Test.setCurrentPage(page);
page.getParameters().put('Action', 'View');

PageReference pg = Page.Mypage2;

pg.getParameters().put('Action', ApexPages.currentPage().getParameters().get('Action'));

ApexPages.currentPage().getParameters().get('Action') == 'View'   

ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR, Label.ERR004));

page

<apex:page standardController="Object_c" action="{!getInfo}" extensions="Controller"  showHeader="false" sidebar="false" standardStylesheets="false" >

apex 

    public Controller(ApexPages.StandardController sc){
    sc.addFields(new List<String>{ 'Field1__c','Field2__c' });
    obj= (Object_c)sc.getRecord();

}