def METHOD_NAME(self) -> None:
    def request_mock(host: str) -> Any:
        request = mock.Mock(spec=["get_host"])
        request.attach_mock(mock.Mock(return_value=host), "get_host")
        return request
    def test(
        expected: str,
        host: str,
        *,
        plusport: bool = True,
        external_host: str = "example.org",
        realm_hosts: Mapping[str, str] = {},
        root_aliases: Sequence[str] = [],
    ) -> None:
        with self.settings(
            EXTERNAL_HOST=external_host,
            REALM_HOSTS=realm_hosts,
            ROOT_SUBDOMAIN_ALIASES=root_aliases,
        ):
            self.assertEqual(get_subdomain(request_mock(host)), expected)
            if plusport and ":" not in host:
                self.assertEqual(get_subdomain(request_mock(host + ":443")), expected)
    ROOT = Realm.SUBDOMAIN_FOR_ROOT_DOMAIN
    # Basics
    test(ROOT, "example.org")
    test("foo", "foo.example.org")
    test(ROOT, "www.example.org", root_aliases=["www"])
    # Unrecognized patterns fall back to root
    test(ROOT, "arbitrary.com")
    test(ROOT, "foo.example.org.evil.com")
    # REALM_HOSTS adds a name,
    test("bar", "chat.barbar.com", realm_hosts={"bar": "chat.barbar.com"})
    # ... exactly, ...
    test(ROOT, "surchat.barbar.com", realm_hosts={"bar": "chat.barbar.com"})
    test(ROOT, "foo.chat.barbar.com", realm_hosts={"bar": "chat.barbar.com"})
    # ... and leaves the subdomain in place too.
    test("bar", "bar.example.org", realm_hosts={"bar": "chat.barbar.com"})
    # Any port is fine in Host if there's none in EXTERNAL_HOST, ...
    test("foo", "foo.example.org:443", external_host="example.org")
    test("foo", "foo.example.org:12345", external_host="example.org")
    # ... but an explicit port in EXTERNAL_HOST must be explicitly matched in Host.
    test(ROOT, "foo.example.org", external_host="example.org:12345")
    test(ROOT, "foo.example.org", external_host="example.org:443", plusport=False)
    test("foo", "foo.example.org:443", external_host="example.org:443")