code: def test_to_numeric_dtype_backend_already_nullable(dtype):
      # GH#50505
      if "pyarrow" in dtype:
          pytest.importorskip("pyarrow")
      ser = Series([1, pd.NA], dtype=dtype)
      result = to_numeric(ser, dtype_backend="numpy_nullable")
      expected = Series([1, pd.NA], dtype=dtype)
      tm.assert_series_equal(result, expected)
  
imports: import decimal
  import numpy
  from numpy import iinfo
  import pytest
  import pandas.util._test_decorators
  import pandas
  from pandas import ArrowDtype, DataFrame, Index, Series, option_context, to_numeric
  import pandas._testing
label_desc: Use image node_id 58 for calling a global function with example usage: test_to_numeric_dtype_backend_already_nullable(dtype) without return types