code: def test_fixed_forward_indexer_count(step):
      # GH: 35579
      df = DataFrame({"b": [None, None, None, 7]})
      indexer = FixedForwardWindowIndexer(window_size=2)
      result = df.rolling(
          window=indexer, min_periods=0, step=step
      ).count()
      expected = DataFrame({"b": [0.0, 0.0, 1.0, 1.0]})[::step]
      tm.assert_frame_equal(result, expected)
  
imports: import numpy
  import pytest
  from pandas import DataFrame, MultiIndex, Series, concat, date_range
  import pandas._testing
  from pandas.api.indexers import BaseIndexer, FixedForwardWindowIndexer
  from pandas.core.indexers.objects import ExpandingIndexer, FixedWindowIndexer, VariableOffsetWindowIndexer
  from pandas.tseries.offsets import BusinessDay
label_desc: Use image node_id 11 for calling a global function with example usage: test_fixed_forward_indexer_count(step) without return types