old_contents: from dimuon import find_pairs
  
  def test_find_pairs():
      particles = None
      pairs = find_pairs(particles)
  
  def test_no_particles():
      particles = []
      pairs = find_pairs(particles)
      assert len(pairs) == 0
      
new_contents: from dimuon import find_pairs
  
  def test_find_pairs():
      particles = None
      pairs = find_pairs(particles)
  
  def test_no_particles():
      particles = []
      pairs = find_pairs(particles)
      assert len(pairs) == 0
  
  def test_one_particle():
      particles = [None]
      pairs = find_pairs(particles)
      assert len(pairs) == 0
  
subject: Test for no pairs from one particle