code: def test_max_len(self):
      res_df1 = self.fpalgo(self.df)
      max_len = np.max(res_df1["itemsets"].apply(len))
      assert max_len == 3
  
      res_df2 = self.fpalgo(self.df, max_len=2)
      max_len = np.max(res_df2["itemsets"].apply(len))
      assert max_len == 2
  
imports: import sys
  from contextlib import contextmanager
  from io import StringIO
  import numpy
  import pandas
  from numpy.testing import assert_array_equal
  from packaging.version import Version
  from pandas import __version__
  from scipy.sparse import csr_matrix
  from mlxtend.preprocessing import TransactionEncoder
  from mlxtend.utils import assert_raises
label_desc: Use image node_id 3 for calling the FPTestEx1All obj's underlying member method code with example usage: obj.test_max_len() without return types