def METHOD_NAME(self, preprocessor):
    """Do grade cells remain unchanged?"""
    preprocessor.lock_solution_cells = False
    preprocessor.lock_grade_cells = False
    preprocessor.lock_all_cells = False
    preprocessor.lock_readonly_cells = False
    cell = create_code_cell()
    cell.metadata['nbgrader'] = {}
    cell.metadata['nbgrader']['grade'] = True
    assert self.deletable(cell)
    assert self.editable(cell)
    new_cell = preprocessor.preprocess_cell(cell, {}, 0)[0]
    assert self.deletable(new_cell)
    assert self.editable(cell)