code: def test_optimizer_base_estimator_string_invalid():
      with pytest.raises(ValueError) as e:
          Optimizer(
              [(-2.0, 2.0)], base_estimator="rtr", n_initial_points=1
          )
      assert "'RF', 'ET', 'GP', 'GBRT' or 'DUMMY'" in str(e.value)
  
imports: import numpy
  import pytest
  from sklearn.multioutput import MultiOutputRegressor
  from numpy.testing import assert_array_equal
  from numpy.testing import assert_equal
  from numpy.testing import assert_raises
  from skopt import gp_minimize
  from skopt import forest_minimize
  from skopt.benchmarks import bench1, bench1_with_time
  from skopt.benchmarks import branin
  from skopt.learning import ExtraTreesRegressor, RandomForestRegressor
  from skopt.learning import GradientBoostingQuantileRegressor
  from skopt.optimizer import Optimizer
  from scipy.optimize import OptimizeResult
label_desc: Use image node_id 16 for calling a global function with example usage: test_optimizer_base_estimator_string_invalid() without return types