message: Reintroduce _proj_on_diag, with a unit test
diff: - YYYY/MM Author: Description of the modification
  """
  +from gudhi.wasserstein.wasserstein import _proj_on_diag
  from gudhi.wasserstein import wasserstein_distance as pot
  from gudhi.hera import wasserstein_distance as hera
  import numpy as np
  @@ -17,6 +18,12 @@ __author__ = "Theo Lacombe"
  __copyright__ = "Copyright (C) 2019 Inria"
  __license__ = "MIT"
  +def test_proj_on_diag():
  + dgm = np.array([[1., 1.], [1., 2.], [3., 5.]])
  + assert np.array_equal(_proj_on_diag(dgm), [[1., 1.], [1.5, 1.5], [4., 4.]])
  + empty = np.empty((0, 2))
  + assert np.array_equal(_proj_on_diag(empty), empty)
  +
  def _basic_wasserstein(wasserstein_distance, delta, test_infinity=True, test_matching=True):
  diag1 = np.array([[2.7, 3.7], [9.6, 14.0], [34.2, 34.974]])
  diag2 = np.array([[2.8, 4.45], [9.5, 14.1]])
  