def test_reduce_terms_auxiliar_functions_manual_input(self):
        """Test reduce_terms function using LiH Hamiltonian."""
        hamiltonian, spectrum = lih_hamiltonian()
        qubit_ham = jordan_wigner(hamiltonian)
        stab1 = QubitOperator('Z0 Z2', -1.0)
        stab2 = QubitOperator('Z1 Z3', -1.0)

        red_ham1, _ = _reduce_terms(terms=qubit_ham,
                                    stabilizer_list=[stab1, stab2],
                                    manual_input=True,
                                    fixed_positions=[0, 1])
        red_ham2, _ = _reduce_terms_keep_length(terms=qubit_ham,
                                                stabilizer_list=[stab1, stab2],
                                                manual_input=True,
                                                fixed_positions=[0, 1])
        red_eigspct1 = eigenspectrum(red_ham1)
        red_eigspct2 = eigenspectrum(red_ham2)

        self.assertAlmostEqual(spectrum[0], red_eigspct1[0])
        self.assertAlmostEqual(spectrum[0], red_eigspct2[0])
 def test_function_errors(self):
     """Test error of main function."""
     hamiltonian, _ = lih_hamiltonian()
     qubit_hamiltonian = jordan_wigner(hamiltonian)
     stab1 = QubitOperator('Z0 Z2', -1.0)
     stab2 = QubitOperator('Z1 Z3', -1.0)
     with self.assertRaises(TypeError):
         reduce_number_of_terms(operator=1, stabilizers=stab1 + stab2)
     with self.assertRaises(TypeError):
         reduce_number_of_terms(operator=qubit_hamiltonian, stabilizers=1)
     with self.assertRaises(TypeError):
         reduce_number_of_terms(operator=qubit_hamiltonian,
                                stabilizers=stab1 + stab2,
                                manual_input=True,
                                fixed_positions=None)
     with self.assertRaises(StabilizerError):
         reduce_number_of_terms(operator=qubit_hamiltonian,
                                stabilizers=stab1 + stab2,
                                manual_input=True,
                                fixed_positions=[1])
     with self.assertRaises(StabilizerError):
         reduce_number_of_terms(operator=qubit_hamiltonian,
                                stabilizers=stab1 + stab2,
                                manual_input=True,
                                fixed_positions=[1, 1])
     with self.assertRaises(StabilizerError):
         # Check Identity as stabilizer error.
         reduce_number_of_terms(operator=qubit_hamiltonian,
                                stabilizers=(stab1 +
                                             QubitOperator(' ', 1.0)))
     with self.assertRaises(StabilizerError):
         # Check complex coefficient stabilizer error.
         reduce_number_of_terms(operator=qubit_hamiltonian,
                                stabilizers=(stab1 +
                                             QubitOperator('Z0', 1.0j)))
     with self.assertRaises(StabilizerError):
         # Check linearly-dependent stabilizer error.
         reduce_number_of_terms(
             operator=qubit_hamiltonian,
             stabilizers=(stab1 + QubitOperator('Z0 Z1 Z2 Z3', 1.0) +
                          stab2))
     with self.assertRaises(StabilizerError):
         # Check anti-commuting stabilizer error.
         reduce_number_of_terms(operator=qubit_hamiltonian,
                                stabilizers=(QubitOperator('X0', 1.0) +
                                             QubitOperator('Y0', 1.0)))
     with self.assertRaises(StabilizerError):
         # Check linearly-dependent stabilizer error.
         _reduce_terms(
             terms=qubit_hamiltonian,
             stabilizer_list=list(stab1 +
                                  QubitOperator('Z0 Z1 Z2 Z3', 1.0) +
                                  stab2),
             manual_input=False,
             fixed_positions=[])
     with self.assertRaises(StabilizerError):
         # Check complex coefficient stabilizer error.
         _reduce_terms(terms=qubit_hamiltonian,
                       stabilizer_list=list(stab1 +
                                            QubitOperator('Z0', 1.0j)),
                       manual_input=False,
                       fixed_positions=[])
     with self.assertRaises(StabilizerError):
         # Check linearly-dependent stabilizer error.
         par_qop = QubitOperator('Z0 Z1 Z2 Z3', 1.0)
         _reduce_terms_keep_length(terms=qubit_hamiltonian,
                                   stabilizer_list=[stab1, par_qop, stab2],
                                   manual_input=False,
                                   fixed_positions=[])
     with self.assertRaises(StabilizerError):
         # Check complex coefficient stabilizer error.
         aux_qop = QubitOperator('Z0', 1.0j)
         _reduce_terms_keep_length(terms=qubit_hamiltonian,
                                   stabilizer_list=[stab1, aux_qop],
                                   manual_input=False,
                                   fixed_positions=[])
     with self.assertRaises(StabilizerError):
         # Test check_commuting_stabilizer function
         # Requires a list of QubitOperators one of which
         # has an imaginary term.
         check_commuting_stabilizers(stabilizer_list=[
             QubitOperator('Z0 Z1', 1.0),
             QubitOperator('X0', 1j)
         ],
                                     msg='This test fails.')
     with self.assertRaises(StabilizerError):
         # Test check_stabilizer_linearity function.
         # Requires a list of QUbitOperators one of which is
         # the identity.
         check_stabilizer_linearity(
             [QubitOperator('Z0 Z1', 1.0),
              QubitOperator(' ', 1.0)],
             msg='This test fails.')