code: def test_length(self, closed, breaks):
      # GH 18789
      index = IntervalIndex.from_breaks(breaks, closed=closed)
      result = index.length
      expected = Index(iv.length for iv in index)
      tm.assert_index_equal(result, expected)
  
      # with NA
      index = index.insert(1, np.nan)
      result = index.length
      expected = Index(iv.length if notna(iv) else iv for iv in index)
      tm.assert_index_equal(result, expected)
  
imports: from itertools import permutations
  import re
  import numpy
  import pytest
  import pandas
  from pandas import Index, Interval, IntervalIndex, Timedelta, Timestamp, date_range, interval_range, isna, notna, timedelta_range
  import pandas._testing
  import pandas.core.common
label_desc: Use image node_id 4 for calling the TestIntervalIndex obj's underlying member method code with example usage: obj.test_length(closed, breaks) without return types