new_contents: """Tests for user utility functions."""
  
  from drudge import Vec, sum_, prod_
  from drudge.term import parse_terms
  
  
  def test_sum_prod_utility():
      """Test the summation and product utility."""
  
      v = Vec('v')
      vecs = [v[i] for i in range(3)]
      v0, v1, v2 = vecs
  
      # The proxy object cannot be directly compared.
      assert parse_terms(sum_(vecs)) == parse_terms(v0 + v1 + v2)
      assert parse_terms(prod_(vecs)) == parse_terms(v0 * v1 * v2)
  
      assert sum_([]) == 0
      assert prod_([]) == 1
  
subject: Add tests for user utilities sum_ and prod_