new_contents: from . import TESTDATADIR
  from .. import Corpus
  
  import random
  
  def test_corpus_instantiate():
      corpus = Corpus(TESTDATADIR)
      assert isinstance(corpus, Corpus)
  
  def test_corpus_len():
      corpus = Corpus(TESTDATADIR)
      assert len(corpus) == 5
  
  def test_corpus_iterator():
      corpus = Corpus(TESTDATADIR)
      article_dois = {article.doi for article in corpus}
      assert article_dois == {
          '10.1371/annotation/3155a3e9-5fbe-435c-a07a-e9a4846ec0b6',
          '10.1371/journal.pbio.2002399',
          '10.1371/journal.pbio.2002354',
          '10.1371/journal.pone.0185809',
          '10.1371/journal.pbio.2001413',
      }
  
  def test_corpus_random_article():
      corpus = Corpus(TESTDATADIR)
      random.seed(1000)
      article = corpus.random_article
      assert article.doi == "10.1371/journal.pone.0185809"
  
subject: add tests for the new corpus functionality