def generate_operator(begin, end):
"""Returns a sum of Z operators at qubit [begin, end)."""
operator = QubitOperator.zero()
for i in range(begin, end):
operator += QubitOperator(((i, 'Z'), ), 1)
return operator
def test_get_operator_groups_empty():
"""Tests get_operator_groups() with zero operator."""
operator = QubitOperator.zero()
operators = list(operator.get_operator_groups(1))
assert operators == []
