Replace assert in reverse_jordan_wigner.py

src/openfermion/transforms/opconversions/reverse_jordan_wigner.py

@@ -81,7 +81,11 @@ def reverse_jordan_wigner(qubit_operator, n_qubits=None):
                     working_term.terms[list(working_term.terms)[0]] = 1.0
 
                 # Get next non-identity operator acting below 'working_qubit'.
-                assert len(working_term.terms) == 1
+                if len(working_term.terms) != 1:
+                    raise ValueError(
+                        'QubitOperator must contain exactly one term. '
+                        f'Found {len(working_term.terms)} terms: {working_term!r}'
+                    )
                 working_qubit = pauli_operator[0] - 1
                 for working_operator in reversed(list(working_term.terms)[0]):
                     if working_operator[0] <= working_qubit:

src/openfermion/transforms/opconversions/reverse_jordan_wigner_test.py

@@ -12,6 +12,7 @@
 """Tests  reverse_jordan_wigner.py."""
 
 import unittest
+from unittest.mock import patch
 
 from openfermion.ops.operators import FermionOperator, QubitOperator
 from openfermion.transforms.opconversions import jordan_wigner, normal_ordered
@@ -160,6 +161,16 @@ def test_bad_type(self):
         with self.assertRaises(TypeError):
             reverse_jordan_wigner(3)
 
+    def test_reverse_jw_multi_term_error(self):
+        with patch(
+            'openfermion.transforms.opconversions.reverse_jordan_wigner.' 'QubitOperator.__mul__'
+        ) as mock_mul:
+            mock_mul.return_value = QubitOperator('X0') + QubitOperator('Y0')
+            with self.assertRaisesRegex(
+                ValueError, 'QubitOperator must contain exactly one term. Found 2 terms'
+            ):
+                reverse_jordan_wigner(QubitOperator('X1'))
+
     def test_jw_convention(self):
         """Test that the Jordan-Wigner convention places the Z-string on
         lower indices."""