new_contents: import pytest
  from ogusa import firm
  import numpy as np
  
  
  def test_get_r():
      # numbers to make calculation easy
      # example of observed parameters:
      # Z     gamma   epsilon  delta  tau_b  delta_tau
      # 1.0   0.35     1.0    0.0975  0.2     0.0975
      Z = 0.5
      gamma = 0.5
      epsilon = 0.5
      delta = 0.25
      tau_b = 0.5
      delta_tau = 1.0
  
      Y = np.array([2.0, 2.0])
      K = np.array([1.0, 1.0])
  
      # test if epsilon == .... works
      # test general accuracy and vector operations
      epsilon = 0.0
      r = firm.get_r(1.0, 1.0, (Z, gamma, epsilon, delta, tau_b, delta_tau))
      # r_test = (1-0.5) * 0.5 - 0.25 = 0
      assert (np.allclose(r, 0.0))
      r = firm.get_r(Y, K, (Z, gamma, epsilon, delta, tau_b, delta_tau))
      assert (np.allclose(r, np.zeros(2)))
  
      epsilon = 0.5
      delta = 0.5
      r = firm.get_r(2.0, 1.0, (Z, gamma, epsilon, delta, tau_b, delta_tau))
      assert (np.allclose(r, 1))
      r = firm.get_r(Y, K, (Z, gamma, epsilon, delta, tau_b, delta_tau))
      assert (np.allclose(r, np.ones(2)))
  
subject: add get_r unit test