Send marker events in all federation tests

The marker event is important to let the remote homeservers
know there are historical messages at the given insertion
event it points to.

It's just a lucky happen-stance that the tests passed before
without the need for the marker event.

Marker events are required/expected in order for the history
to be properly visible on remote homservers.

Author: MadLittleMods

tests/msc2716_test.go

@@ -575,6 +575,11 @@ func TestImportHistoricalMessages(t *testing.T) {
 			)
 			batchSendResBody := client.ParseJSON(t, batchSendRes)
 			historicalEventIDs := client.GetJSONFieldStringArray(t, batchSendResBody, "event_ids")
+			baseInsertionEventID := client.GetJSONFieldStr(t, batchSendResBody, "base_insertion_event_id")
+
+			// Send the marker event which lets remote homeservers know there are
+			// some historical messages back at the given insertion event.
+			sendMarkerAndEnsureBackfilled(t, as, alice, roomID, baseInsertionEventID)
 
 			// Join the room from a remote homeserver after the historical messages were sent
 			remoteCharlie.JoinRoom(t, roomID, []string{"hs1"})
@@ -654,6 +659,10 @@ func TestImportHistoricalMessages(t *testing.T) {
 			batchSendResBody := client.ParseJSON(t, batchSendRes)
 			historicalEventIDs := client.GetJSONFieldStringArray(t, batchSendResBody, "event_ids")
 
+			// Send the marker event which lets remote homeservers know there are
+			// some historical messages back at the given insertion event.
+			sendMarkerAndEnsureBackfilled(t, as, alice, roomID, insertionEventID)
+
 			// Join the room from a remote homeserver after the historical messages were sent
 			remoteCharlie.JoinRoom(t, roomID, []string{"hs1"})
 
@@ -756,7 +765,8 @@ func TestImportHistoricalMessages(t *testing.T) {
 				},
 			})
 
-			// Send the marker event
+			// Send the marker event which lets remote homeservers know there are
+			// some historical messages back at the given insertion event.
 			sendMarkerAndEnsureBackfilled(t, as, remoteCharlie, roomID, baseInsertionEventID)
 
 			// FIXME: In the future, we should probably replace the following logic
@@ -849,7 +859,8 @@ func TestImportHistoricalMessages(t *testing.T) {
 				},
 			})
 
-			// Send the marker event
+			// Send the marker event which lets remote homeservers know there are
+			// some historical messages back at the given insertion event.
 			sendMarkerAndEnsureBackfilled(t, as, remoteCharlie, roomID, baseInsertionEventID)
 
 			// FIXME: In the future, we should probably replace the following logic
@@ -959,7 +970,8 @@ func TestImportHistoricalMessages(t *testing.T) {
 				batchEventID := client.GetJSONFieldStr(t, batchSendResBody, "batch_event_id")
 				baseInsertionEventID := client.GetJSONFieldStr(t, batchSendResBody, "base_insertion_event_id")
 
-				// Send the marker event
+				// Send the marker event which lets remote homeservers know there are
+				// some historical messages back at the given insertion event.
 				markerEventID := sendMarkerAndEnsureBackfilled(t, as, alice, roomID, baseInsertionEventID)
 
 				redactEventID(t, alice, roomID, insertionEventID, 403)
@@ -1110,11 +1122,11 @@ func ensureVirtualUserRegistered(t *testing.T, c *client.CSAPI, virtualUserLocal
 	}
 }
 
+// Send the marker event which lets remote homeservers know there are
+// some historical messages back at the given insertion event.
 func sendMarkerAndEnsureBackfilled(t *testing.T, as *client.CSAPI, c *client.CSAPI, roomID, insertionEventID string) (markerEventID string) {
 	t.Helper()
 
-	// Send a marker event to let all of the homeservers know about the
-	// insertion point where all of the historical messages are at
 	markerEvent := b.Event{
 		Type: markerEventType,
 		Content: map[string]interface{}{