code: def test_error_with_prefix_contains_unassigned(
      dummies_with_unassigned,
  ):
      with pytest.raises(
          ValueError,
          match=(
              r"Dummy DataFrame contains unassigned value\(s\); "
              r"First instance in row: 2"
          ),
      ):
          from_dummies(dummies_with_unassigned, sep="_")
  
imports: import numpy
  import pytest
  from pandas import DataFrame, Series, from_dummies, get_dummies
  import pandas._testing
label_desc: Use image node_id 11 for calling a global function with example usage: test_error_with_prefix_contains_unassigned(dummies_with_unassigned) without return types