Some_Test.cls

@isTest
public with sharing class Some_Test {
    @testSetup static void setup() {
        Account acc = new Account(Name = 'account1');
        insert acc;
        System.debug(acc.Id); // We can confirm Account Id on the debug log.
    }

    @isTest static void testMethod1() {
        List<Account> accs = [SELECT Id FROM Account];
        for (Account acc : accs) {
            System.debug(acc.Id); // We can confirm Account Id. NullPointerException is avoided!!
        }
    }
}