Add reproduction of the situation for a Synapse consistency issue

Reproduction test for element-hq/synapse#18075

tests/csapi/synapse_consistency_test.go

@@ -0,0 +1,36 @@
+package csapi_tests
+
+import (
+	"testing"
+
+	"github.com/matrix-org/complement"
+	"github.com/matrix-org/complement/client"
+	"github.com/matrix-org/complement/helpers"
+)
+
+func TestSynapseConsistency(t *testing.T) {
+	numHomeservers := 2
+	deployment := complement.Deploy(t, numHomeservers)
+	defer deployment.Destroy(t)
+
+	alice := deployment.Register(t, "hs1", helpers.RegistrationOpts{LocalpartSuffix: "alice"})
+
+	charlie1 := deployment.Register(t, "hs2", helpers.RegistrationOpts{LocalpartSuffix: "charlie1"})
+	charlie2 := deployment.Register(t, "hs2", helpers.RegistrationOpts{LocalpartSuffix: "charlie2"})
+
+	t.Run("test1", func(t *testing.T) {
+		// Create a room on hs1
+		roomID := alice.MustCreateRoom(t, map[string]interface{}{
+			"preset": "private_chat",
+		})
+
+		// Invite multiple users from hs2
+		alice.MustInviteRoom(t, roomID, charlie1.UserID)
+		charlie1.MustSyncUntil(t, client.SyncReq{}, client.SyncInvitedTo(charlie1.UserID, roomID))
+		charlie1.MustJoinRoom(t, roomID, []string{"hs1"})
+
+		alice.MustInviteRoom(t, roomID, charlie2.UserID)
+		charlie2.MustSyncUntil(t, client.SyncReq{}, client.SyncInvitedTo(charlie2.UserID, roomID))
+		charlie2.MustJoinRoom(t, roomID, []string{"hs1"})
+	})
+}