new_contents: """Test basic Wick expansion of terms.
  
  The tests in the module is attempted to test the core Wick facility on terms,
  without parallelization by Spark.
  """
  
  from sympy import symbols, IndexedBase
  
  from drudge import Range, Vec, CR, AN, FERMI, FockDrudge
  from drudge.term import sum_term
  from drudge.wick import wick_expand
  
  
  def test_wick_expansion_of_term(spark_ctx):
      """Test the basic Wick expansion facility on a single term."""
  
      dr = FockDrudge(spark_ctx, exch=FERMI)
  
      op_base = Vec('f')
      f = op_base[AN]
      f_dag = op_base[CR]
  
      a, b, c, d = symbols('a b c d')
      r = Range('L')
      t = IndexedBase('t')
      u = IndexedBase('u')
  
      term = sum_term(
          (a, r), (b, r), (c, r), (d, r),
          t[a, b] * u[c, d] * f_dag[a] * f[b] * f_dag[c] * f[d]
      )[0]
  
      res = wick_expand(
          term, comparator=dr.comparator, contractor=dr.contractor,
          phase=dr.phase
      )
      assert len(res) == 2
  
      # Simplify the result a little.
  
      dumms = {r: [a, b, c, d]}
  
      res = {
          i.simplify_deltas([lambda x: r])
              .canon(vec_colour=dr.vec_colour)
              .reset_dumms(dumms)[0]
          for i in res
          }
  
      expected = {
          sum_term(
              (a, r), (b, r), (c, r), (d, r),
              t[a, c] * u[b, d] * f_dag[a] * f_dag[b] * f[d] * f[c]
          )[0],
          sum_term(
              (a, r), (b, r), (c, r),
              t[a, c] * u[c, b] * f_dag[a] * f[b]
          )[0]
      }
  
      assert (res == expected)
  
subject: Add test for basic Wick expansion facility