old_contents: import os
  
  import pandas as pd
  import root_pandas
  
  
  def test_issue_60():
      df = pd.DataFrame({'a': list(range(10)), 'b': list(range(10))})
      root_pandas.to_root(df, 'tmp_1.root', 'my_tree_1')
      root_pandas.to_root(df, 'tmp_2.root', 'my_tree')
      result = root_pandas.read_root(['tmp_1.root', 'tmp_2.root'], 'my_tree', warn_missing_tree=True)
      assert len(result) == 10
      os.remove('tmp_1.root')
      os.remove('tmp_2.root')
  
  
  def test_issue_63():
      df = pd.DataFrame({'a': [], 'b': []})
      root_pandas.to_root(df, 'tmp_1.root', 'my_tree')
      df = pd.DataFrame({'a': list(range(10)), 'b': list(range(10))})
      root_pandas.to_root(df, 'tmp_2.root', 'my_tree')
      result = list(root_pandas.read_root(['tmp_1.root', 'tmp_2.root'], 'my_tree', where='a > 2', chunksize=1))
      assert len(result) == 7
      assert all(len(df) == 1 for df in result)
      os.remove('tmp_1.root')
      os.remove('tmp_2.root')
  
new_contents: import os
  
  import pandas as pd
  import root_pandas
  
  
  def test_issue_60():
      df = pd.DataFrame({'a': list(range(10)), 'b': list(range(10))})
      root_pandas.to_root(df, 'tmp_1.root', 'my_tree_1')
      root_pandas.to_root(df, 'tmp_2.root', 'my_tree')
      result = root_pandas.read_root(['tmp_1.root', 'tmp_2.root'], 'my_tree', warn_missing_tree=True)
      assert len(result) == 10
      os.remove('tmp_1.root')
      os.remove('tmp_2.root')
  
  
  def test_issue_63():
      df = pd.DataFrame({'a': [], 'b': []})
      root_pandas.to_root(df, 'tmp_1.root', 'my_tree')
      df = pd.DataFrame({'a': list(range(10)), 'b': list(range(10))})
      root_pandas.to_root(df, 'tmp_2.root', 'my_tree')
      result = list(root_pandas.read_root(['tmp_1.root', 'tmp_2.root'], 'my_tree', where='a > 2', chunksize=1))
      assert len(result) == 7
      assert all(len(df) == 1 for df in result)
      os.remove('tmp_1.root')
      os.remove('tmp_2.root')
  
  
  def test_issue_80():
      df = pd.DataFrame({'a': [1, 2], 'b': [4, 5]})
      df.columns = ['a', 'a']
      try:
          root_pandas.to_root(df, '/tmp/example.root')
      except ValueError as e:
          assert 'DataFrame contains duplicated column names' in e.args[0]
      else:
          raise Exception('ValueError is expected')
  
  
  def test_issue_82():
      variables = ['MET_px', 'MET_py', 'EventWeight']
      df = root_pandas.read_root('http://scikit-hep.org/uproot/examples/HZZ.root', 'events', columns=variables)
      assert list(df.columns) == variables
  
subject: Add tests