code: def test_error_estimation_complex(solver_class):
      h = 0.2
      solver = solver_class(
          lambda t, y: 1j * y, 0, [1j], 1, first_step=h
      )
      solver.step()
      err_norm = solver._estimate_error_norm(solver.K, h, scale=[1])
      assert np.isrealobj(err_norm)
  
file_path: catboost/contrib/python/scipy/py3/scipy/integrate/_ivp/tests/test_rk.py
imports: import pytest
  from numpy.testing import assert_allclose, assert_
  import numpy
  from scipy.integrate import RK23, RK45, DOP853
  from scipy.integrate._ivp import dop853_coefficients
label_desc: Use image node_id 4 for calling a global function with example usage: test_error_estimation_complex(solver_class) without return types