hi, I got the output for the above scenario this is the code which worked well .

Trigger:

      trigger AccountsDelete on Account (After delete) {
    list<Id> I=new list<Id>();
    for(account a:trigger.old){
        I.add(a.Id);
    }
    if(trigger.isDelete){
        system.debug('hello am in trigger');
        if(system.isFuture()==False){
            HttpRequest req = new HttpRequest();
            req.setTimeout(2000);
            Accounts_Trigger_Helper.DeleteAccount(i);
        }
    }
}

HelperClass:
            global class Accounts_Trigger_Helper {
    @future
    global static void DeleteAccount(list<ID> acclist) {
        system.debug('hello am in Helper');
        HttpRequest req = new HttpRequest();
        req.setTimeout(2000);
        system.debug('acclist'+acclist);
        list<account> deletedacc=new list<account>();
        deletedacc = [select id,name,phone from Account where
                      isDeleted=true and Id =:acclist ALL rows];
        system.debug('deletedacc'+deletedacc);
        if(!deletedacc.isEmpty()){
            undelete deletedacc;
        }
    }
}

Test Class:

@isTest
public class Accounts_Trigger_Test {

    public static  testmethod void DeleteAccountTest(){
        test.startTest();
        account acc=new account();
        acc.name='Krishna';
        acc.Phone='84615';
        insert acc;
        delete acc;
        System.assertEquals('Krishna',acc.Name,'Name is not equal');
        test.stopTest();
    }
}