new_contents: from nose.tools import eq_
  from mhctools import BindingPrediction, BindingPredictionCollection
  
  def test_collection_to_dataframe():
      bp = BindingPrediction(
          peptide="SIINFEKL",
          allele="A0201",
          affinity=1.5,
          percentile_rank=0.1)
      collection = BindingPredictionCollection([bp])
      df = collection.to_dataframe()
      eq_(df.peptide.iloc[0], "SIINFEKL")
      eq_(df.affinity.iloc[0], 1.5)
      eq_(df.allele.iloc[0], "A0201")
      eq_(df.percentile_rank.iloc[0], 0.1)
  
subject: add test for collection