code: def test_cummax():
      for array in arrays:
          s = Stream.source(array, dtype="float")
          w = s.cummax(skipna=True).rename("w")
          expected = list(pd.Series(array).cummax(skipna=True))
  
          assert_op([w], expected)
  
      for array in arrays:
          s = Stream.source(array, dtype="float")
          w = s.cummin(skipna=False).rename("w")
          expected = list(pd.Series(array).cummin(skipna=False))
  
          assert_op([w], expected)
  
imports: import numpy
  import pandas
  from tensortrade.feed import Stream
  from tests.utils.ops import assert_op
label_desc: Use image node_id 4 for calling a global function with example usage: test_cummax() without return types