class_docstr: Test that warnings are raised e.g. for an ill-conditioned
  Fourier transform during the reconstruction.
docstr: Test that a warning is raised for an ill-conditioned matrix in the Fourier trafo.
docstr_tok: ["Test","that","a","warning","is","raised","for","an","ill-conditioned","matrix","in","the","Fourier","trafo","."]
code: def test_ill_conditioned(self):
      """Test that a warning is raised for an ill-conditioned matrix in the Fourier trafo."""
      shifts = [
          -np.pi / 2 - 1e-9,
          -np.pi / 2,
          0,
          np.pi / 2,
          np.pi / 2 + 1e-9,
      ]
      with pytest.warns(
          UserWarning, match="condition number of the Fourier"
      ):
          _reconstruct_gen(
              dummy_qnode, spectrum=[1.0, 2.0], shifts=shifts
          )
  
imports: from inspect import signature
  from itertools import chain
  from functools import reduce
  import pytest
  import numpy
  import pennylane
  from pennylane import numpy
  from pennylane.fourier.reconstruct import _reconstruct_equ, _reconstruct_gen, _prepare_jobs, reconstruct
  from pennylane.fourier.utils import join_spectra
label_desc: Use image node_id 1 for calling the TestWarnings obj's underlying member method code with example usage: obj.test_ill_conditioned() without return types