How to use the everett.manager.ConfigOSEnv function in everett

def test_ConfigOSEnv():
    os.environ["EVERETT_TEST_FOO"] = "bar"
    os.environ["EVERETT_TEST_FOO"] = "bar"
    cose = ConfigOSEnv()

    assert cose.get("everett_test_foo") == "bar"
    assert cose.get("EVERETT_test_foo") == "bar"
    assert cose.get("foo", namespace=["everett", "test"]) == "bar"

def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.ENVIRON = EnvironProxy(
            ConfigManager(
                [
                    ConfigOSEnv(),
                    ConfigEnvFileEnv(".env"),
                    DumbConfigIniEnv([os.environ.get("ARA_CFG"), "~/.config/ara/server.cfg", "/etc/ara/server.cfg"]),
                ]
            ).with_namespace("ara")
        )

home = os.path.expanduser('~')
            rv_home = os.path.join(home, '.rastervision')
        self.rv_home = rv_home

        config_file_locations = self._discover_config_file_locations(profile)

        help_doc = ('Check https://docs.rastervision.io/ for docs.')
        self.config = ConfigManager(
            # Specify one or more configuration environments in
            # the order they should be checked
            [
                # Allow overrides
                ConfigDictEnv(config_overrides),

                # Looks in OS environment first
                ConfigOSEnv(),

                # Look for an .env file
                ConfigEnvFileEnv('.env'),

                # Looks in INI files in order specified
                ConfigIniEnv(config_file_locations),
            ],

            # Make it easy for users to find your configuration docs
            doc=help_doc)

def get_config():
    return ConfigManager(
        [
            ConfigIniEnv([
                os.environ.get('CIS_CONFIG_INI'),
                '~/.mozilla-cis.ini',
                '/etc/mozilla-cis.ini'
            ]),
            ConfigOSEnv()
        ]

def get_config():
    return ConfigManager(
        [ConfigIniEnv([os.environ.get("CIS_CONFIG_INI"), "~/.mozilla-cis.ini", "/etc/mozilla-cis.ini"]), ConfigOSEnv()]
    )

def get_config():
    return ConfigManager(
        [
            ConfigIniEnv([
                os.environ.get('THREATRESPONSE_INI'),
                '~/.threatresponse.ini',
                '/etc/threatresponse.ini'
            ]),
            ConfigOSEnv()
        ]

def get_config():
    return ConfigManager(
        [
            ConfigOSEnv()
        ]