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)
  
subject: Add test case for AcousticMaterial.