def METHOD_NAME():
    """Idle qubits must be preserved even if the input has barriers.
    Test input:
         ┌───┐ ░
    q_0: ┤ X ├─░─
         └───┘ ░
    q_1: ──────░─
         ┌───┐ ░
    q_2: ┤ X ├─░─
         └───┘ ░
    q_3: ────────
    Expected output:
         ┌───┐
    q_0: ┤ X ├
         └───┘
    q_1: ─────
         ┌───┐
    q_2: ┤ X ├
         └───┘
    q_3: ─────
    """
    test_circuit_qiskit = qiskit.QuantumCircuit(4)
    test_circuit_qiskit.x(0)
    test_circuit_qiskit.x(2)
    test_circuit_qiskit.barrier(0, 1, 2)
    test_copy = test_circuit_qiskit.copy()
    scaled = scaling_function(test_circuit_qiskit)
    # Mitiq is expected to remove qiskit barriers
    expected = qiskit.QuantumCircuit(4)
    expected.x(0)
    expected.x(2)
    assert scaled == expected
    # Mitiq should not mutate the input circuit
    assert test_circuit_qiskit == test_copy