old_contents: import os
  
  from astropy import units as u
  import numpy as np
  import pytest
  
  import tardis
  from tardis.io.model_reader import (read_artis_density, 
  read_simple_ascii_abundances)
  
  data_path = os.path.join(tardis.__path__[0], 'io', 'tests', 'data')
  
  @pytest.fixture
  def artis_density_fname():
      return os.path.join(data_path, 'artis_model.dat')
  
  @pytest.fixture
  def artis_abundances_fname():
      return os.path.join(data_path, 'artis_abundances.dat')
  
  def test_simple_read_artis_density(artis_density_fname):
      (time_of_model, index, v_inner, v_outer,
          mean_density) = read_artis_density(artis_density_fname)
  
      assert np.isclose(0.00114661 * u.day, time_of_model, atol=1e-7 * u.day)
      assert np.isclose(mean_density[23], 0.2250048 * u.g / u.cm**3, atol=1.e-6
          * u.g / u.cm**3)
      assert len(mean_density) == 69
      assert len(mean_density) == len(v_inner)
  
  # Artis files are currently read with read ascii files function
  def test_read_simple_ascii_abundances(artis_abundances_fname):
      index, abundances = read_simple_ascii_abundances(artis_abundances_fname)
      assert len(abundances.columns) == 69
      assert np.isclose(abundances[23].ix[2], 2.672351e-08 , atol=1.e-12)
  
new_contents: import os
  
  from astropy import units as u
  import numpy as np
  import pytest
  
  import tardis
  from tardis.io.model_reader import (read_artis_density, 
  read_simple_ascii_abundances)
  
  data_path = os.path.join(tardis.__path__[0], 'io', 'tests', 'data')
  
  @pytest.fixture
  def artis_density_fname():
      return os.path.join(data_path, 'artis_model.dat')
  
  @pytest.fixture
  def artis_abundances_fname():
      return os.path.join(data_path, 'artis_abundances.dat')
  
  def test_simple_read_artis_density(artis_density_fname):
      time_of_model, velocity, mean_density = read_artis_density(artis_density_fname)
  
      assert np.isclose(0.00114661 * u.day, time_of_model, atol=1e-7 * u.day)
      assert np.isclose(mean_density[23], 0.2250048 * u.g / u.cm**3, atol=1.e-6
          * u.g / u.cm**3)
      assert len(mean_density) == 69
      assert len(velocity) == len(mean_density) + 1
  
  # Artis files are currently read with read ascii files function
  def test_read_simple_ascii_abundances(artis_abundances_fname):
      index, abundances = read_simple_ascii_abundances(artis_abundances_fname)
      assert len(abundances.columns) == 69
      assert np.isclose(abundances[23].ix[2], 2.672351e-08 , atol=1.e-12)
  
subject: Adjust io/tests/test_model_reader to the changed model_reader.