test: Populate eg.initialSnapshot.realmCanDeleteOwnMessageGroup by default

But only when we're simulating recent servers, as the comment says.
(FL 291 removed realmDeleteOwnMessagePolicy and added
realmCanDeleteOwnMessageGroup, so to be representative, tests should
always specify one but not the other.)

Author: chrisbobbe

test/example_data.dart

@@ -1285,6 +1285,13 @@ InitialSnapshot initialSnapshot({
   List<User>? realmNonActiveUsers,
   List<User>? crossRealmBots,
 }) {
+  if (realmDeleteOwnMessagePolicy == null) {
+    // Set a default for realmCanDeleteOwnMessageGroup, but only if we're
+    // trying to simulate a modern server without realmDeleteOwnMessagePolicy.
+    realmCanDeleteOwnMessageGroup ??= GroupSettingValueNamed(nobodyGroup.id);
+  }
+  assert((realmCanDeleteOwnMessageGroup != null) ^ (realmDeleteOwnMessagePolicy != null));
+
   return InitialSnapshot(
     queueId: queueId ?? '1:2345',
     lastEventId: lastEventId ?? -1,
@@ -1320,7 +1327,6 @@ InitialSnapshot initialSnapshot({
     userTopics: userTopics,
     // no default; allow `null` to simulate servers without this
     realmCanDeleteAnyMessageGroup: realmCanDeleteAnyMessageGroup,
-    // no default; allow `null` to simulate servers without this
     realmCanDeleteOwnMessageGroup: realmCanDeleteOwnMessageGroup,
     realmDeleteOwnMessagePolicy: realmDeleteOwnMessagePolicy,
     realmWildcardMentionPolicy: realmWildcardMentionPolicy ?? RealmWildcardMentionPolicy.everyone,