code: def test_series_unique():
      for size in [10**x for x in range(5)]:
          arr = np.random.randint(low=-1, high=10, size=size)
          mask = arr != -1
          sr = cudf.Series(arr)
          sr[~mask] = None
          assert set(arr[mask]) == set(sr.unique().dropna().to_numpy())
          assert len(set(arr[mask])) == sr.nunique()
  
imports: from concurrent.futures import ThreadPoolExecutor
  import cupy
  import numpy
  import pandas
  import pytest
  import cudf
  from cudf.datasets import randomdata
  from cudf.testing._utils import _create_cudf_series_float64_default, _create_pandas_series_float64_default, assert_eq, assert_exceptions_equal, expect_warning_if
label_desc: Use image node_id 4 for calling a global function with example usage: test_series_unique() without return types