def METHOD_NAME(data, upgrader):
    #Get the settings from the original file.
    original_parser = configparser.ConfigParser(interpolation = None)
    original_parser.read_string(data["file_data"])
    settings = set()
    if original_parser.has_section("general") and "visible_settings" in original_parser["general"]:
        settings = set(original_parser["general"]["visible_settings"].split(";"))
    #Perform the upgrade.
    _, upgraded_preferences = upgrader.upgradePreferences(data["file_data"], "<string>")
    upgraded_preferences = upgraded_preferences[0]
    #Find whether the removed setting is removed from the file now.
    settings -= VersionUpgrade25to26._removed_settings
    parser = configparser.ConfigParser(interpolation = None)
    parser.read_string(upgraded_preferences)
    assert (parser.has_section("general") and "visible_settings" in parser["general"]) == (len(settings) > 0) #If there are settings, there must also be a preference.
    if settings:
        assert settings == set(parser["general"]["visible_settings"].split(";"))