Add check_generator to assert_valid

pennylane/operation.py

@@ -1449,7 +1449,7 @@ def generator(self): # pylint: disable=no-self-use
  0.5 * Y(0) + Z(0) @ X(1)
 
  The generator may also be provided in the form of a dense or sparse Hamiltonian
- (using :class:`.Hermitian` and :class:`.SparseHamiltonian` respectively).
+ (using :class:`.Hamiltonian` and :class:`.SparseHamiltonian` respectively).
 
  The default value to return is ``None``, indicating that the operation has
  no defined generator.

pennylane/ops/functions/assert_valid.py

@@ -169,6 +169,25 @@ def _check_eigendecomposition(op):
  assert qml.math.allclose(decomp_mat, original_mat), failure_comment
 
 
+def _check_generator(op):
+ """Checks that if an operator has a generator, it does."""
+
+ if op.has_generator:
+ gen = op.generator()
+ assert isinstance(gen, qml.Hamiltonian) or isinstance(gen, qml.ops.SparseHamiltonian)
+ new_op = qml.exp(gen, 1j * op.data[0])
+ assert qml.math.allclose(
+ qml.matrix(op, wire_order=op.wires), qml.matrix(new_op, wire_order=op.wires)
+ )
+ else:
+ failure_comment = (
+ "If has_generator is False, the matrix method must raise a ``GeneratorUndefinedError``."
+ )
+ _assert_error_raised(
+ op.matrix, qml.operation.GeneratorUndefinedError, failure_comment=failure_comment
+ )()
+
+
 def _check_copy(op):
  """Check that copies and deep copies give identical objects."""
  copied_op = copy.copy(op)
@@ -333,4 +352,5 @@ def __init__(self, wires):
  _check_matrix(op)
  _check_matrix_matches_decomp(op)
  _check_eigendecomposition(op)
+ _check_generator(op)
  _check_capture(op)