code: def test_max_len(self):
      res_df1 = fpmax(self.df)
      max_len = np.max(res_df1["itemsets"].apply(len))
      assert max_len == 3
  
      res_df2 = fpmax(self.df, max_len=2)
      max_len = np.max(res_df2["itemsets"].apply(len))
      assert max_len == 2
  
imports: import unittest
  import numpy
  import pandas
  from test_fpbase import FPTestEdgeCases, FPTestErrors, FPTestEx1, FPTestEx2, FPTestEx3All, compare_dataframes
  from mlxtend.frequent_patterns import fpmax
label_desc: Use image node_id 3 for calling the TestEx1 obj's underlying member method code with example usage: obj.test_max_len() without return types