new_contents: """ module for the class for core of the application """
  
  import pytest
  from click.testing import CliRunner
  from exch.core import cli
  from exch.helpers import fixer, google_finance_converter
  
  @pytest.fixture
  def runner():
      return CliRunner()
  
  def test_same_currency_code():
      """ when the same currency is base as well as target """
      result_usd = runner().invoke(cli, ['-f', 'USD', '-t', 'USD'])
      assert result_usd.exit_code == 0
      assert result_usd.output == "1.00\n"
  
      result_inr = runner().invoke(cli, ['-f', 'INR', '-t', 'INR'])
      assert result_inr.exit_code == 0
      assert result_inr.output == "1.00\n"
  
  def test_fixer_usd_to_inr_():
      """ base: USD, target: INR, on the date of 2017-05-12 """
      assert fixer('USD', 'INR', date='2017-05-12') == round(64.307, 2)
  
  def test_fixer_usd_to_jpy_():
      """ base: USD, target: JPY, on the date of 2017-05-12 """
      assert fixer('USD', 'JPY', date='2017-05-12') == round(113.85, 2)
  
  
  #def test_fixer_inavlid_currency():
  #    """ when invalid currency is passed to fixer.io """
  #    pass
  
  #def test_fixer_invalid_value_type():
  #    """ when invalid value type is passed to fixer """
  #    pass
  
subject: add basic tests