code: def test_fillna():
      array = [-1, np.nan, -3, 4, np.nan]
  
      s = Stream.source(array, dtype="float")
  
      w = s.fillna(-1).rename("w")
      expected = list(pd.Series(array).fillna(-1))
  
      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 1 for calling a global function with example usage: test_fillna() without return types