old_contents: var index = require('./index.js');
  
  test('Nationalcode must be valid', ()=>{
      expect(index.isValid('1111111111')).toBe(true);
  })
  
new_contents: var index = require('./index.js');
  
  test('Nationalcode must be valid', ()=>{
      expect(index.isValid('1111111111')).toBe(true);
  });
  
  test('Nationalcode must not be valid', ()=>{
      expect(index.isValid('7512698452')).toBe(false);
  });
subject: fix some bugs in test file