def METHOD_NAME(self):
    """
    Ensure BoundLogger is immutable by default.
    """
    b = build_bl(processors=[KeyValueRenderer(sort_keys=True)])
    b = b.bind(x=42, y=23)
    b1 = b.bind(foo="bar")
    b2 = b.bind(foo="qux")
    assert b._context != b1._context != b2._context