new_contents: """Test that we can read and write bib entries with postprocessing."""
  
  import bibpy
  import pytest
  
  
  @pytest.fixture
  def test_string():
      return """@article{key,
          author   = {James Conway and Archer Sterling and},
          xdata    = {key1, key2,key3,     key4, key5  ,},
          urldate  = {2017-01-14},
          keywords = {parsing; computer science   ; databases;  },
          year     = {1957},
          month    = {11},
          msg      = "Part of " # var # " string",
          foreword = {Jan Leo {and} the Editors}
      }"""
  
  
  def test_processing_invariant(test_string):
      entry = bibpy.read_string(test_string, 'relaxed',
                                postprocess=True).entries[0]
  
      assert entry.author == ['James Conway', 'Archer Sterling']
      assert entry.xdata == ['key1', 'key2', 'key3', 'key4', 'key5']
      assert entry.urldate == bibpy.date.DateRange.fromstring('2017-01-14')
      assert entry.keywords == ['parsing', 'computer science', 'databases']
      assert entry.year == 1957
      assert entry.month == 'November'
      assert entry.msg == '"Part of " # var # " string"'
      assert entry.foreword == ['Jan Leo and the Editors']
  
      entry = bibpy.read_string(bibpy.write_string([entry]), 'relaxed',
                                postprocess=True).entries[0]
  
      assert entry.xdata == ['key1', 'key2', 'key3', 'key4', 'key5']
      assert entry.urldate == bibpy.date.DateRange.fromstring('2017-01-14')
      assert entry.keywords == ['parsing', 'computer science', 'databases']
      assert entry.year == 1957
      assert entry.month == 'November'
      assert entry.msg == '"Part of " # var # " string"'
      assert entry.foreword == ['Jan Leo and the Editors']
  
subject: Add test for processing invariant