code: def test_case_when_single_condition(df):
      """
      Test output on a single condition.
      """
      result = Series([np.nan, np.nan, np.nan]).case_when(
          [(df.a.eq(1), 1)]
      )
      expected = Series([1, np.nan, np.nan])
      tm.assert_series_equal(result, expected)
  
file_path: pandas/pandas/tests/series/methods/test_case_when.py
imports: import numpy
  import pytest
  from pandas import DataFrame, Series, array, date_range
  import pandas._testing
label_desc: Use image node_id 6 for calling a global function with example usage: test_case_when_single_condition(df) without return types