Try (but fail) to demonstrate the longname behavior

setup.py

@@ -111,7 +111,7 @@ install_requires = [
     "pyrsistent",
 
     # A great way to define types of values.
-    "attrs >= 18.2.0",
+    "attrs >= 20.1.0",
 
     # WebSocket library for twisted and asyncio
     "autobahn >= 22.4.3",

src/allmydata/storage_client.py

@@ -39,6 +39,7 @@ from os import urandom
 from configparser import NoSectionError
 
 import attr
+from attr import define
 from hyperlink import DecodedURL
 from zope.interface import (
     Attribute,
@@ -637,6 +638,7 @@ class _FoolscapStorage(object):
 
 
 @implementer(IFoolscapStorageServer)
+@define
 class _NullStorage(object):
     """
     Abstraction for *not* communicating with a storage server of a type with
@@ -650,7 +652,7 @@ class _NullStorage(object):
     lease_seed = hashlib.sha256(b"").digest()
 
     name = "<unsupported>"
-    longname = "<storage with unsupported protocol>"
+    longname: str = "<storage with unsupported protocol>"
 
     def connect_to(self, tub, got_connection):
         return NonReconnector()
@@ -784,9 +786,7 @@ def _make_storage_system(
         )
     except MissingPlugin as e:
         _log.failure("Missing plugin")
-        ns = _NullStorage()
-        ns.longname = '<missing plugin "{}">'.format(e.args[0])
-        return ns
+        return _NullStorage('<missing plugin "{}">'.format(e.args[0]))
     else:
         return _FoolscapStorage.from_announcement(
             server_id,

src/allmydata/test/test_storage_client.py

@@ -159,7 +159,7 @@ class GetConnectionStatus(unittest.TestCase):
         self.assertTrue(IConnectionStatus.providedBy(connection_status))
 
 
-class UnrecognizedAnnouncement(unittest.TestCase):
+class UnrecognizedAnnouncement(SyncTestCase):
     """
     Tests for handling of announcements that aren't recognized and don't use
     *anonymous-storage-FURL*.
@@ -169,9 +169,14 @@ class UnrecognizedAnnouncement(unittest.TestCase):
     an announcement generated by a storage server plugin which is not loaded
     in the client.
     """
+    plugin_name = u"tahoe-lafs-testing-v1"
     ann = {
-        u"name": u"tahoe-lafs-testing-v1",
-        u"any-parameter": 12345,
+        u"storage-options": [
+            {
+                u"name": plugin_name,
+                u"any-parameter": 12345,
+            },
+        ],
     }
     server_id = b"abc"
 
@@ -234,6 +239,15 @@ class UnrecognizedAnnouncement(unittest.TestCase):
         server.get_foolscap_write_enabler_seed()
         server.get_nickname()
 
+    def test_longname(self) -> None:
+        """
+        ``NativeStorageServer.get_longname`` describes the missing plugin.
+        """
+        server = self.native_storage_server()
+        self.assertThat(
+            server.get_longname(),
+            Equals('<missing plugin "{}">'.format(self.plugin_name)),
+        )
 
 
 class PluginMatchedAnnouncement(SyncTestCase):