Hi Please Help Me how to write a test class for my controller.

public class ImpactedIssuerController {


public ImpactedIssuerController(ApexPages.StandardController controller){ 

 
}
   
     Public String cid;
     public List<WrapIssuer> wrapIssuerList {get; set;}
     public Boolean selectAllCheckbox {get; set;}  
     public boolean errormsg=false; 
    
     String userinput;
     String userinp;
     String userinp2;
     String siloinput;
    
     public List<Issuers__c> allissuer = new List<Issuers__c>();
     public List<Issuers__c> selectedIssuer2 = new List<Issuers__c>();
     
     
     /* Getter and setter methods for getting the user input ie. Issuer name from the UI */
     public String getuserinput(){return userinput;}
     //public void setuserinput(String userinp){this.userinput=userinp=userinp2;}
     public void setuserinput(String userinp){this.userinput=userinp;}
     public String getuserinp(){return userinp;}
     public void setuserinp(String userinp){this.userinp=userinp;} 
     
     public String getuserinp2(){return userinp2;}
     public void setuserinp2(String userinp2){this.userinp2=userinp2;} 
     
     public String getsiloinput(){return siloinput;}
     public void setsiloinput(String siloinput){this.siloinput=siloinput;}
     
     
      /*End of Getter and Setter methods */
      
      
     /* Method to Search the Issuer database to fetch the query results */
      public List<Issuers__c> search() {
      
      errormsg=false;
      wrapIssuerList = new List<WrapIssuer>();
      for(Issuers__c ilist:[select Name,id,Bankdir_Name__c,Processor_Name__c,Subprocessor_Name__c,Silo_Name__c  from Issuers__c where Name like :userinput+'%' and Processor_Name__c like :userinp+'%' and Subprocessor_Name__c like :userinp2+'%' and Silo_Name__c like :siloinput+'%'LIMIT 1000 ])
        {
           wrapIssuerList.add(new WrapIssuer(ilist));
         }
         return null;
      }
      /* End of Search method */
       
       /* Method for returning the contact search results to the UI */
        public List<WrapIssuer> getresults()
            {
             return wrapIssuerList;
            }
        /* End of Method */
        
        
        /* Wrapper class to contain contact record and a boolean flag */
        public class WrapIssuer {
        public Issuers__c Issu {get; set;}
        public Boolean selected {get; set;}
 
        public WrapIssuer(Issuers__c ism) {
            Issu = ism;
            selected = false;
         }
        }
       /* end of Wrapper class */
       
       
      /* Method to fetch the selected records and save them to other another object*/
      
   public List<Impacted_Issuers__c> cList=new List<Impacted_Issuers__c>();
    
    public PageReference processSelected() {
    List<Issuers__c> selectedIssuers = new List<Issuers__c>();
    //selectedIssuer= new List<Issuers__c>();
 
        for(wrapIssuer wrapIssuerObj : wrapIssuerList) {
            if(wrapIssuerObj.selected == true) {
                selectedIssuers.add(wrapIssuerObj.Issu);
            }
        }
    
     for(Issuers__c Issu:selectedIssuers){
     Impacted_Issuers__c imp =new Impacted_Issuers__c();
        imp.Name=Issu.name;
        imp.Bankdir_Name__c=Issu.Bankdir_Name__c;
        imp.Processor_Name__c=Issu.Processor_Name__c;
        imp.Subprocessor_Name__c=Issu.Subprocessor_Name__c;
        imp.Silo_Name__c=Issu.Silo_Name__c;
        imp.Development_Task__c =string.valueOf(apexpages.currentpage().getparameters().get('CF00N1F000002a29R_lkid'));
        cList.add(imp);
        
            
     }   
if(cList.size()>0)
{
     insert cList; 
     return new PageReference('/'+ApexPages.currentPage().getParameters().get('CF00N1F000002a29R_lkid'));
     }
     
        errormsg=true;
         return null;        
    }
       
    
       /* return error message if no contact is selected */
        public boolean geterrormsg()
        {
         return errormsg;
        } 
        
        /* Method to cancel the entire process */
        public Pagereference Cancel()
        {
        return new PageReference('/'+ApexPages.currentPage().getParameters().get('CF00N1F000002a29R_lkid'));
        }
        
    }