old_contents: import numpy as np
  import pyfds as fds
  
  
  def test_acoustic_material():
      water = fds.AcousticMaterial(1500, 1000)
      water.bulk_viscosity = 1e-3
      water.shear_viscosity = 1e-3
      assert np.isclose(water.absorption_coef, 7e-3 / 3)
  
  
  def test_acoustic1d_create_matrices():
      fld = fds.Acoustic1D(t_delta=1, t_samples=1,
                           x_delta=1, x_samples=3,
                           material=fds.AcousticMaterial(700, 0.01, bulk_viscosity=1))
      fld.create_matrices()
      assert np.allclose(fld.a_p_v.toarray(), [[-4900, 4900, 0], [0, -4900, 4900], [0, 0, -4900]])
      assert np.allclose(fld.a_v_p.toarray(), [[100, 0, 0], [-100, 100, 0], [0, -100, 100]])
      assert np.allclose(fld.a_v_v.toarray(), [[-200, 100, 0], [100, -200, 100], [0, 100, -200]])
  
new_contents: import numpy as np
  import pyfds as fds
  
  
  def test_acoustic_material():
      water = fds.AcousticMaterial(1500, 1000)
      water.bulk_viscosity = 1e-3
      water.shear_viscosity = 1e-3
      assert np.isclose(water.absorption_coef, 7e-3 / 3)
  
  
  def test_acoustic1d_create_matrices():
      fld = fds.Acoustic1D(t_delta=1, t_samples=1,
                           x_delta=1, x_samples=3,
                           material=fds.AcousticMaterial(700, 0.01, bulk_viscosity=1))
      fld.create_matrices()
      assert np.allclose(fld.a_p_v.toarray(), [[-4900, 4900, 0], [0, -4900, 4900], [0, 0, -4900]])
      assert np.allclose(fld.a_v_p.toarray(), [[100, 0, 0], [-100, 100, 0], [0, -100, 100]])
      assert np.allclose(fld.a_v_v.toarray(), [[-200, 100, 0], [100, -200, 100], [0, 100, -200]])
  
  
  def test_acoustic2d_create_matrices():
      fld = fds.Acoustic2D(t_delta=1, t_samples=1,
                           x_delta=1, x_samples=2,
                           y_delta=1, y_samples=2,
                           material=fds.AcousticMaterial(700, 0.01, bulk_viscosity=1))
      fld.create_matrices()
      assert np.allclose(fld.a_p_vx.toarray(), [[-4900, 4900, 0, 0], [0, -4900, 4900, 0],
                                                [0, 0, -4900, 4900], [0, 0, 0, -4900]])
      assert np.allclose(fld.a_p_vy.toarray(), [[-4900, 0, 4900, 0], [0, -4900, 0, 4900],
                                                [0, 0, -4900, 0], [0, 0, 0, -4900]])
      assert np.allclose(fld.a_vx_p.toarray(), [[100, 0, 0, 0], [-100, 100, 0, 0], [0, -100, 100, 0],
                                                [0, 0, -100, 100]])
      assert np.allclose(fld.a_vy_p.toarray(), [[100, 0, 0, 0], [0, 100, 0, 0], [-100, 0, 100, 0],
                                                [0, -100, 0, 100]])
      assert np.allclose(fld.a_vx_vx.toarray(), [[-400, 100, 100, 0], [100, -400, 100, 100],
                                                 [100, 100, -400, 100], [0, 100, 100, -400]])
      assert np.allclose(fld.a_vy_vy.toarray(), [[-400, 100, 100, 0], [100, -400, 100, 100],
                                                 [100, 100, -400, 100], [0, 100, 100, -400]])
  
subject: Add test case for Acoustic2D.create_matrices().