text: from types import SimpleNamespace
  import numpy.testing as npt
  from fluxpart.wue import water_use_efficiency
  
  
  def test_water_use_efficiency():
      """ Unit test does not guarantee the wue function is correct, but if
      this fails, something has changed, and better understand why.
      """
  
      hf_stats = SimpleNamespace(
          rho_vapor=9.607e-3,
          rho_co2=658.8e-6,
          T=28.56 + 273.15,
          P=100.1e3,
          cov_w_q=0.1443e-3,
          cov_w_c=-1.059e-6,
          cov_w_T=0.1359,
          ustar=0.4179,
          rho_totair=1.150,
      )
  
      wue = water_use_efficiency(
          hf_stats,
          meas_ht=7.11,
          canopy_ht=4.42,
          ppath="C3",
          ci_mod="const_ppm",
          diff_ratio=(1 / 0.7),
      )
  
      npt.assert_allclose(wue.wue, -6.45e-3, atol=0.005e-3)
      npt.assert_allclose(wue.ambient_h2o, 12.4e-3, atol=0.05e-3)
      npt.assert_allclose(wue.ambient_co2, 638.e-6, atol=0.5e-6)
      npt.assert_allclose(wue.inter_h2o, 28.3e-3, atol=0.05e-3)
      npt.assert_allclose(wue.inter_co2, 492.e-6, atol=0.5e-6)
  
  
  if __name__ == "__main__":
      test_water_use_efficiency()
  