code: def test_no_prefix_string_cats_basic():
      dummies = DataFrame(
          {"a": [1, 0, 0, 1], "b": [0, 1, 0, 0], "c": [0, 0, 1, 0]}
      )
      expected = DataFrame({"": ["a", "b", "c", "a"]})
      result = from_dummies(dummies)
      tm.assert_frame_equal(result, expected)
  
imports: import numpy
  import pytest
  from pandas import DataFrame, Series, from_dummies, get_dummies
  import pandas._testing
label_desc: Use image node_id 20 for calling a global function with example usage: test_no_prefix_string_cats_basic() without return types