code: def test_series_at():
      arr = Categorical(["a", "b", "c"])
      ser = Series(arr)
      result = ser.at[0]
      assert result == "a"
  
imports: import math
  import numpy
  import pytest
  from pandas import NA, Categorical, CategoricalIndex, Index, Interval, IntervalIndex, NaT, PeriodIndex, Series, Timedelta, Timestamp
  import pandas._testing
  import pandas.core.common
label_desc: Use image node_id 4 for calling a global function with example usage: test_series_at() without return types