diff --git a/internal/api/client.go b/internal/api/client.go
index 36797e6..71bb708 100644
--- a/internal/api/client.go
+++ b/internal/api/client.go
@@ -33,11 +33,6 @@ type Client interface {
 	// uploaded to the server. Failure to block will result in flakey tests as other users may not
 	// encrypt for this Client due to not detecting keys for the Client.
 	Login(t ct.TestLike, opts ClientCreationOpts) error
-	// MustStartSyncing to begin syncing from sync v2 / sliding sync.
-	// Tests should call stopSyncing() at the end of the test.
-	// MUST BLOCK until the initial sync is complete.
-	// Fails the test if there was a problem syncing.
-	MustStartSyncing(t ct.TestLike) (stopSyncing func())
 	// StartSyncing to begin syncing from sync v2 / sliding sync.
 	// Tests should call stopSyncing() at the end of the test.
 	// MUST BLOCK until the initial sync is complete.
@@ -96,9 +91,31 @@ type Client interface {
 	Opts() ClientCreationOpts
 }
 
-type Notification struct {
-	Event
-	HasMentions *bool
+// TestClient is a Client with extra helper functions added to make writing tests easier.
+// Client implementations are not expected to implement these helper functions, and are
+// instead composed together by the test rig itself. See TestClientImpl.
+type TestClient interface {
+	Client
+	MustStartSyncing(t ct.TestLike) (stopSyncing func())
+}
+
+func NewTestClient(c Client) TestClient {
+	return &testClientImpl{
+		Client: c,
+	}
+}
+
+type testClientImpl struct {
+	Client
+}
+
+func (c *testClientImpl) MustStartSyncing(t ct.TestLike) (stopSyncing func()) {
+	t.Helper()
+	stopSyncing, err := c.StartSyncing(t)
+	if err != nil {
+		ct.Fatalf(t, "MustStartSyncing: %s", err)
+	}
+	return stopSyncing
 }
 
 type LoggedClient struct {
@@ -136,14 +153,6 @@ func (c *LoggedClient) MustGetEvent(t ct.TestLike, roomID, eventID string) Event
 	return c.Client.MustGetEvent(t, roomID, eventID)
 }
 
-func (c *LoggedClient) MustStartSyncing(t ct.TestLike) (stopSyncing func()) {
-	t.Helper()
-	c.Logf(t, "%s MustStartSyncing starting to sync", c.logPrefix())
-	stopSyncing = c.Client.MustStartSyncing(t)
-	c.Logf(t, "%s MustStartSyncing now syncing", c.logPrefix())
-	return
-}
-
 func (c *LoggedClient) StartSyncing(t ct.TestLike) (stopSyncing func(), err error) {
 	t.Helper()
 	c.Logf(t, "%s StartSyncing starting to sync", c.logPrefix())
@@ -216,6 +225,11 @@ func (c *LoggedClient) logPrefix() string {
 	return fmt.Sprintf("[%s](%s)", c.UserID(), c.Type())
 }
 
+type Notification struct {
+	Event
+	HasMentions *bool
+}
+
 // ClientCreationOpts are options to use when creating crypto clients.
 //
 // This contains a mixture of generic options which can be used across any client, and specific
diff --git a/internal/api/js/js.go b/internal/api/js/js.go
index 5ae0294..b421d68 100644
--- a/internal/api/js/js.go
+++ b/internal/api/js/js.go
@@ -549,13 +549,6 @@ func (c *JSClient) MustGetEvent(t ct.TestLike, roomID, eventID string) api.Event
 	return ev
 }
 
-func (c *JSClient) MustStartSyncing(t ct.TestLike) (stopSyncing func()) {
-	t.Helper()
-	stopSyncing, err := c.StartSyncing(t)
-	must.NotError(t, "StartSyncing", err)
-	return stopSyncing
-}
-
 // StartSyncing to begin syncing from sync v2 / sliding sync.
 // Tests should call stopSyncing() at the end of the test.
 func (c *JSClient) StartSyncing(t ct.TestLike) (stopSyncing func(), err error) {
diff --git a/internal/api/rust/rust.go b/internal/api/rust/rust.go
index 44db503..bd3cf1f 100644
--- a/internal/api/rust/rust.go
+++ b/internal/api/rust/rust.go
@@ -323,13 +323,6 @@ func (c *RustClient) MustGetEvent(t ct.TestLike, roomID, eventID string) api.Eve
 	return *ev
 }
 
-func (c *RustClient) MustStartSyncing(t ct.TestLike) (stopSyncing func()) {
-	t.Helper()
-	stopSyncing, err := c.StartSyncing(t)
-	must.NotError(t, "StartSyncing", err)
-	return stopSyncing
-}
-
 // StartSyncing to begin syncing from sync v2 / sliding sync.
 // Tests should call stopSyncing() at the end of the test.
 func (c *RustClient) StartSyncing(t ct.TestLike) (stopSyncing func(), err error) {
diff --git a/internal/cc/test_context.go b/internal/cc/test_context.go
index 169b356..8711215 100644
--- a/internal/cc/test_context.go
+++ b/internal/cc/test_context.go
@@ -70,9 +70,9 @@ func (c *TestContext) RegisterNewUser(t *testing.T, clientType api.ClientType, l
 //
 // The callback function is invoked after this, and cleanup functions are called on your behalf when the
 // callback function ends.
-func (c *TestContext) WithClientSyncing(t *testing.T, req *ClientCreationRequest, callback func(cli api.Client)) {
+func (c *TestContext) WithClientSyncing(t *testing.T, req *ClientCreationRequest, callback func(cli api.TestClient)) {
 	t.Helper()
-	c.WithClientsSyncing(t, []*ClientCreationRequest{req}, func(clients []api.Client) {
+	c.WithClientsSyncing(t, []*ClientCreationRequest{req}, func(clients []api.TestClient) {
 		callback(clients[0])
 	})
 }
@@ -87,9 +87,9 @@ func (c *TestContext) WithClientSyncing(t *testing.T, req *ClientCreationRequest
 //
 // The callback function is invoked after this, and cleanup functions are called on your behalf when the
 // callback function ends.
-func (c *TestContext) WithClientsSyncing(t *testing.T, reqs []*ClientCreationRequest, callback func(clients []api.Client)) {
+func (c *TestContext) WithClientsSyncing(t *testing.T, reqs []*ClientCreationRequest, callback func(clients []api.TestClient)) {
 	t.Helper()
-	cryptoClients := make([]api.Client, len(reqs))
+	cryptoClients := make([]api.TestClient, len(reqs))
 	// Login all clients BEFORE starting any of their sync loops.
 	// We do this because Login will send device list updates and cause clients to upload OTKs/device keys.
 	// We want to make sure ALL these keys are on the server before any test client syncs otherwise it
@@ -107,18 +107,18 @@ func (c *TestContext) WithClientsSyncing(t *testing.T, reqs []*ClientCreationReq
 }
 
 // mustCreateMultiprocessClient creates a new RPC process and instructs it to create a client given by the client creation options.
-func (c *TestContext) mustCreateMultiprocessClient(t *testing.T, req *ClientCreationRequest) api.Client {
+func (c *TestContext) mustCreateMultiprocessClient(t *testing.T, req *ClientCreationRequest) api.TestClient {
 	t.Helper()
 	if c.RPCBinaryPath == "" {
 		t.Skipf("RPC binary path not provided, skipping multiprocess test. To run this test, set COMPLEMENT_CRYPTO_RPC_BINARY")
-		return nil
+		return api.NewTestClient(nil)
 	}
 	ctxPrefix := fmt.Sprintf("%d", c.RPCInstance.Add(1))
 	remoteBindings, err := rpc.NewLanguageBindings(c.RPCBinaryPath, req.User.ClientType.Lang, ctxPrefix)
 	if err != nil {
 		t.Fatalf("Failed to create new RPC language bindings: %s", err)
 	}
-	return remoteBindings.MustCreateClient(t, req.Opts)
+	return api.NewTestClient(remoteBindings.MustCreateClient(t, req.Opts))
 }
 
 // WithAliceSyncing is a helper function which creates a rust/js client and automatically logs in Alice and starts
@@ -126,7 +126,7 @@ func (c *TestContext) mustCreateMultiprocessClient(t *testing.T, req *ClientCrea
 //
 // The callback function is invoked after this, and cleanup functions are called on your behalf when the
 // callback function ends.
-func (c *TestContext) WithAliceSyncing(t *testing.T, callback func(alice api.Client)) {
+func (c *TestContext) WithAliceSyncing(t *testing.T, callback func(alice api.TestClient)) {
 	t.Helper()
 	must.NotEqual(t, c.Alice, nil, "No Alice defined. Call CreateTestContext() with at least 1 api.ClientType.")
 	c.WithClientSyncing(t, &ClientCreationRequest{
@@ -139,7 +139,7 @@ func (c *TestContext) WithAliceSyncing(t *testing.T, callback func(alice api.Cli
 //
 // The callback function is invoked after this, and cleanup functions are called on your behalf when the
 // callback function ends.
-func (c *TestContext) WithAliceAndBobSyncing(t *testing.T, callback func(alice, bob api.Client)) {
+func (c *TestContext) WithAliceAndBobSyncing(t *testing.T, callback func(alice, bob api.TestClient)) {
 	t.Helper()
 	must.NotEqual(t, c.Bob, nil, "No Bob defined. Call CreateTestContext() with at least 2 api.ClientTypes.")
 	c.WithClientsSyncing(t, []*ClientCreationRequest{
@@ -149,7 +149,7 @@ func (c *TestContext) WithAliceAndBobSyncing(t *testing.T, callback func(alice,
 		{
 			User: c.Bob,
 		},
-	}, func(clients []api.Client) {
+	}, func(clients []api.TestClient) {
 		callback(clients[0], clients[1])
 	})
 }
@@ -159,7 +159,7 @@ func (c *TestContext) WithAliceAndBobSyncing(t *testing.T, callback func(alice,
 //
 // The callback function is invoked after this, and cleanup functions are called on your behalf when the
 // callback function ends.
-func (c *TestContext) WithAliceBobAndCharlieSyncing(t *testing.T, callback func(alice, bob, charlie api.Client)) {
+func (c *TestContext) WithAliceBobAndCharlieSyncing(t *testing.T, callback func(alice, bob, charlie api.TestClient)) {
 	t.Helper()
 	must.NotEqual(t, c.Charlie, nil, "No Charlie defined. Call CreateTestContext() with at least 3 api.ClientTypes.")
 	c.WithClientsSyncing(t, []*ClientCreationRequest{
@@ -172,7 +172,7 @@ func (c *TestContext) WithAliceBobAndCharlieSyncing(t *testing.T, callback func(
 		{
 			User: c.Charlie,
 		},
-	}, func(clients []api.Client) {
+	}, func(clients []api.TestClient) {
 		callback(clients[0], clients[1], clients[2])
 	})
 }
@@ -288,7 +288,7 @@ func (c *TestContext) MustRegisterNewDevice(t *testing.T, user *User, newDeviceI
 }
 
 // MustLoginClient is the same as MustCreateClient but also logs in the client.
-func (c *TestContext) MustLoginClient(t *testing.T, req *ClientCreationRequest) api.Client {
+func (c *TestContext) MustLoginClient(t *testing.T, req *ClientCreationRequest) api.TestClient {
 	t.Helper()
 	client := c.MustCreateClient(t, req)
 	must.NotError(t, "failed to login client", client.Login(t, client.Opts()))
@@ -297,7 +297,7 @@ func (c *TestContext) MustLoginClient(t *testing.T, req *ClientCreationRequest)
 
 // MustCreateClient creates an api.Client from an existing Complement client and the specified client type. Additional options
 // can be set to configure the client beyond that of the Complement client e.g to add persistent storage.
-func (c *TestContext) MustCreateClient(t *testing.T, req *ClientCreationRequest) api.Client {
+func (c *TestContext) MustCreateClient(t *testing.T, req *ClientCreationRequest) api.TestClient {
 	t.Helper()
 	if req.User == nil {
 		ct.Fatalf(t, "MustCreateClient: ClientCreationRequest missing 'user', register one with RegisterNewUser or use an existing one.")
@@ -318,11 +318,11 @@ func (c *TestContext) MustCreateClient(t *testing.T, req *ClientCreationRequest)
 // mustCreateClient creates an api.Client with the specified language/server, else fails the test.
 //
 // Options can be provided to configure clients, such as enabling persistent storage.
-func mustCreateClient(t *testing.T, clientType api.ClientType, cfg api.ClientCreationOpts) api.Client {
+func mustCreateClient(t *testing.T, clientType api.ClientType, cfg api.ClientCreationOpts) api.TestClient {
 	bindings := langs.GetLanguageBindings(clientType.Lang)
 	if bindings == nil {
 		t.Fatalf("unknown language: %s", clientType.Lang)
 	}
 	c := bindings.MustCreateClient(t, cfg)
-	return c
+	return api.NewTestClient(c)
 }
diff --git a/internal/deploy/rpc/client.go b/internal/deploy/rpc/client.go
index 2f07061..02ab2fa 100644
--- a/internal/deploy/rpc/client.go
+++ b/internal/deploy/rpc/client.go
@@ -218,24 +218,6 @@ func (c *RPCClient) Login(t ct.TestLike, opts api.ClientCreationOpts) error {
 	return err
 }
 
-// MustStartSyncing to begin syncing from sync v2 / sliding sync.
-// Tests should call stopSyncing() at the end of the test.
-// MUST BLOCK until the initial sync is complete.
-// Fails the test if there was a problem syncing.
-func (c *RPCClient) MustStartSyncing(t ct.TestLike) (stopSyncing func()) {
-	var void int
-	err := c.client.Call("Server.MustStartSyncing", t.Name(), &void)
-	if err != nil {
-		t.Fatalf("RPCClient.MustStartSyncing: %s", err)
-	}
-	return func() {
-		err := c.client.Call("Server.StopSyncing", t.Name(), &void)
-		if err != nil {
-			t.Fatalf("RPCClient.StopSyncing: %s", err)
-		}
-	}
-}
-
 // StartSyncing to begin syncing from sync v2 / sliding sync.
 // Tests should call stopSyncing() at the end of the test.
 // MUST BLOCK until the initial sync is complete.
diff --git a/internal/deploy/rpc/server.go b/internal/deploy/rpc/server.go
index 1c83d14..0e363d3 100644
--- a/internal/deploy/rpc/server.go
+++ b/internal/deploy/rpc/server.go
@@ -111,12 +111,6 @@ func (s *Server) Login(opts api.ClientCreationOpts, void *int) error {
 	return s.activeClient.Login(&api.MockT{}, opts)
 }
 
-func (s *Server) MustStartSyncing(testName string, void *int) error {
-	defer s.keepAlive()
-	s.stopSyncing = s.activeClient.MustStartSyncing(&api.MockT{TestName: testName})
-	return nil
-}
-
 func (s *Server) StartSyncing(testName string, void *int) error {
 	defer s.keepAlive()
 	stopSyncing, err := s.activeClient.StartSyncing(&api.MockT{TestName: testName})
diff --git a/internal/tests/client_test.go b/internal/tests/client_test.go
index 72502d9..c000301 100644
--- a/internal/tests/client_test.go
+++ b/internal/tests/client_test.go
@@ -29,7 +29,7 @@ var (
 	ssDeployment *deploy.SlidingSyncDeployment
 	// aka functions which make clients, and we don't care about the language.
 	// Tests just loop through this array for each client impl.
-	clientFactories []func(t *testing.T, cfg api.ClientCreationOpts) api.Client
+	clientFactories []func(t *testing.T, cfg api.ClientCreationOpts) api.TestClient
 )
 
 func Deploy(t *testing.T) *deploy.SlidingSyncDeployment {
@@ -47,30 +47,30 @@ func Deploy(t *testing.T) *deploy.SlidingSyncDeployment {
 }
 
 func TestMain(m *testing.M) {
-	rustClientCreator := func(t *testing.T, cfg api.ClientCreationOpts) api.Client {
+	rustClientCreator := func(t *testing.T, cfg api.ClientCreationOpts) api.TestClient {
 		client, err := rust.NewRustClient(t, cfg)
 		if err != nil {
 			t.Fatalf("NewRustClient: %s", err)
 		}
-		return client
+		return api.NewTestClient(client)
 	}
-	jsClientCreator := func(t *testing.T, cfg api.ClientCreationOpts) api.Client {
+	jsClientCreator := func(t *testing.T, cfg api.ClientCreationOpts) api.TestClient {
 		client, err := js.NewJSClient(t, cfg)
 		if err != nil {
 			t.Fatalf("NewJSClient: %s", err)
 		}
-		return client
+		return api.NewTestClient(client)
 	}
 	clientFactories = append(clientFactories, rustClientCreator, jsClientCreator)
 
 	rpcBinary := os.Getenv("COMPLEMENT_CRYPTO_RPC_BINARY")
 	if rpcBinary != "" {
-		clientFactories = append(clientFactories, func(t *testing.T, cfg api.ClientCreationOpts) api.Client {
+		clientFactories = append(clientFactories, func(t *testing.T, cfg api.ClientCreationOpts) api.TestClient {
 			remoteBindings, err := rpc.NewLanguageBindings(rpcBinary, api.ClientTypeRust, "")
 			if err != nil {
 				log.Fatal(err)
 			}
-			return remoteBindings.MustCreateClient(t, cfg)
+			return api.NewTestClient(remoteBindings.MustCreateClient(t, cfg))
 		})
 	}
 	rust.SetupLogs("rust_sdk_logs")
@@ -104,7 +104,7 @@ func TestReceiveTimeline(t *testing.T) {
 	}
 
 	// test that if we start syncing with a room full of events, we see those events.
-	ForEachClient(t, "existing_events", deployment, func(t *testing.T, client api.Client, csapi *client.CSAPI) {
+	ForEachClient(t, "existing_events", deployment, func(t *testing.T, client api.TestClient, csapi *client.CSAPI) {
 		must.NotError(t, "Failed to login", client.Login(t, client.Opts()))
 		roomID, eventIDs := createAndSendEvents(t, csapi)
 		time.Sleep(time.Second) // give time for everything to settle server-side e.g sliding sync proxy
@@ -132,7 +132,7 @@ func TestReceiveTimeline(t *testing.T) {
 	})
 
 	// test that if we are already syncing and then see a room live stream full of events, we see those events.
-	ForEachClient(t, "live_events", deployment, func(t *testing.T, client api.Client, csapi *client.CSAPI) {
+	ForEachClient(t, "live_events", deployment, func(t *testing.T, client api.TestClient, csapi *client.CSAPI) {
 		must.NotError(t, "Failed to login", client.Login(t, client.Opts()))
 		stopSyncing := client.MustStartSyncing(t)
 		defer stopSyncing()
@@ -171,7 +171,7 @@ func TestReceiveTimeline(t *testing.T) {
 
 func TestCanWaitUntilEventInRoomBeforeRoomIsKnown(t *testing.T) {
 	deployment := Deploy(t)
-	ForEachClient(t, "", deployment, func(t *testing.T, client api.Client, csapi *client.CSAPI) {
+	ForEachClient(t, "", deployment, func(t *testing.T, client api.TestClient, csapi *client.CSAPI) {
 		roomID := csapi.MustCreateRoom(t, map[string]interface{}{})
 		eventID := csapi.SendEventSynced(t, roomID, b.Event{
 			Type: "m.room.message",
@@ -196,7 +196,7 @@ func TestCanWaitUntilEventInRoomBeforeRoomIsKnown(t *testing.T) {
 
 func TestSendingEvents(t *testing.T) {
 	deployment := Deploy(t)
-	ForEachClient(t, "", deployment, func(t *testing.T, client api.Client, csapi *client.CSAPI) {
+	ForEachClient(t, "", deployment, func(t *testing.T, client api.TestClient, csapi *client.CSAPI) {
 		must.NotError(t, "Failed to login", client.Login(t, client.Opts()))
 		roomID := csapi.MustCreateRoom(t, map[string]interface{}{})
 		stopSyncing := client.MustStartSyncing(t)
@@ -217,7 +217,7 @@ func TestSendingEvents(t *testing.T) {
 }
 
 // run a subtest for each client factory
-func ForEachClient(t *testing.T, name string, deployment *deploy.SlidingSyncDeployment, fn func(t *testing.T, client api.Client, csapi *client.CSAPI)) {
+func ForEachClient(t *testing.T, name string, deployment *deploy.SlidingSyncDeployment, fn func(t *testing.T, client api.TestClient, csapi *client.CSAPI)) {
 	for _, createClient := range clientFactories {
 		csapiAlice := deployment.Register(t, "hs1", helpers.RegistrationOpts{
 			LocalpartSuffix: "client",
diff --git a/tests/delayed_requests_test.go b/tests/delayed_requests_test.go
index 4ff5f26..4720084 100644
--- a/tests/delayed_requests_test.go
+++ b/tests/delayed_requests_test.go
@@ -33,7 +33,7 @@ func TestDelayedInviteResponse(t *testing.T) {
 	Instance().ForEachClientType(t, func(t *testing.T, clientType api.ClientType) {
 		tc := Instance().CreateTestContext(t, clientType, clientType)
 		roomID := tc.CreateNewEncryptedRoom(t, tc.Alice)
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			// we send a message first so clients which lazily call /members can do so now.
 			// if we don't do this, the client won't rely on /sync for the member list so won't fail.
 			alice.SendMessage(t, roomID, "dummy message to make /members call")
diff --git a/tests/device_keys_test.go b/tests/device_keys_test.go
index b18ad08..9ada72a 100644
--- a/tests/device_keys_test.go
+++ b/tests/device_keys_test.go
@@ -41,7 +41,7 @@ func TestFailedDeviceKeyDownloadRetries(t *testing.T) {
 			roomID := tc.CreateNewEncryptedRoom(t, tc.Alice, cc.EncRoomOptions.Invite([]string{tc.Bob.UserID}))
 			tc.Bob.MustJoinRoom(t, roomID, []string{"hs1"})
 
-			tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+			tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 				// When Alice sends a message
 				alice.SendMessage(t, roomID, "checking whether we can send a message")
 
diff --git a/tests/federation_connectivity_test.go b/tests/federation_connectivity_test.go
index 4b6b624..e72958e 100644
--- a/tests/federation_connectivity_test.go
+++ b/tests/federation_connectivity_test.go
@@ -32,7 +32,7 @@ func TestNewUserCannotGetKeysForOfflineServer(t *testing.T) {
 		t.Logf("%s joining room %s", tc.Bob.UserID, roomID)
 		tc.Bob.MustJoinRoom(t, roomID, []string{"hs1"})
 
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			// let clients sync device keys
 			time.Sleep(time.Second)
 
@@ -50,7 +50,7 @@ func TestNewUserCannotGetKeysForOfflineServer(t *testing.T) {
 			tc.Alice.MustInviteRoom(t, roomID, tc.Charlie.UserID)
 			tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 				User: tc.Charlie,
-			}, func(charlie api.Client) {
+			}, func(charlie api.TestClient) {
 				tc.Charlie.MustJoinRoom(t, roomID, []string{"hs1"})
 
 				// let charlie sync device keys... and fail to get bob's keys!
@@ -116,7 +116,7 @@ func TestExistingSessionCannotGetKeysForOfflineServer(t *testing.T) {
 		tc.Bob.MustJoinRoom(t, roomIDab, []string{"hs1"})
 		tc.Bob.MustJoinRoom(t, roomIDbc, []string{"hs1"})
 
-		tc.WithAliceBobAndCharlieSyncing(t, func(alice, bob, charlie api.Client) {
+		tc.WithAliceBobAndCharlieSyncing(t, func(alice, bob, charlie api.TestClient) {
 			// let clients sync device keys
 			time.Sleep(time.Second)
 
diff --git a/tests/key_backup_test.go b/tests/key_backup_test.go
index d267f3c..62c9c43 100644
--- a/tests/key_backup_test.go
+++ b/tests/key_backup_test.go
@@ -36,7 +36,7 @@ func TestCanBackupKeys(t *testing.T) {
 
 		// SDK testing below
 		// -----------------
-		tc.WithAliceSyncing(t, func(backupCreator api.Client) {
+		tc.WithAliceSyncing(t, func(backupCreator api.TestClient) {
 			body := "An encrypted message"
 			waiter := backupCreator.WaitUntilEventInRoom(t, roomID, api.CheckEventHasBody(body))
 			evID := backupCreator.SendMessage(t, roomID, body)
@@ -98,7 +98,7 @@ func TestBackupWrongRecoveryKeyFails(t *testing.T) {
 
 		// SDK testing below
 		// -----------------
-		tc.WithAliceSyncing(t, func(backupCreator api.Client) {
+		tc.WithAliceSyncing(t, func(backupCreator api.TestClient) {
 			body := "An encrypted message"
 			waiter := backupCreator.WaitUntilEventInRoom(t, roomID, api.CheckEventHasBody(body))
 			evID := backupCreator.SendMessage(t, roomID, body)
diff --git a/tests/membership_acls_test.go b/tests/membership_acls_test.go
index 42a1cb9..a7dd54c 100644
--- a/tests/membership_acls_test.go
+++ b/tests/membership_acls_test.go
@@ -35,7 +35,7 @@ func TestAliceBobEncryptionWorks(t *testing.T) {
 		// SDK testing below
 		// -----------------
 
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			wantMsgBody := "Hello world"
 
 			// Check the room is in fact encrypted
@@ -75,7 +75,7 @@ func TestCanDecryptMessagesAfterInviteButBeforeJoin(t *testing.T) {
 
 		// SDK testing below
 		// -----------------
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			wantMsgBody := "Message sent when bob is invited not joined"
 
 			// Check the room is in fact encrypted
@@ -122,7 +122,7 @@ func TestBobCanSeeButNotDecryptHistoryInPublicRoom(t *testing.T) {
 
 		// SDK testing below
 		// -----------------
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			// Alice sends a message which Bob should not be able to decrypt
 			beforeJoinBody := "Before Bob joins"
 			waiter := alice.WaitUntilEventInRoom(t, roomID, api.CheckEventHasBody(beforeJoinBody))
@@ -163,7 +163,7 @@ func TestOnRejoinBobCanSeeButNotDecryptHistoryInPublicRoom(t *testing.T) {
 
 		// SDK testing below
 		// -----------------
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			// Alice sends a message which Bob should be able to decrypt.
 			bothJoinedBody := "Alice and Bob in a room"
 			waiter := bob.WaitUntilEventInRoom(t, roomID, api.CheckEventHasBody(bothJoinedBody))
@@ -222,7 +222,7 @@ func TestOnNewDeviceBobCanSeeButNotDecryptHistoryInPublicRoom(t *testing.T) {
 		// SDK testing below
 		// -----------------
 
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			// Alice sends a message which Bob should be able to decrypt.
 			onlyFirstDeviceBody := "Alice and Bob in a room"
 			waiter := bob.WaitUntilEventInRoom(t, roomID, api.CheckEventHasBody(onlyFirstDeviceBody))
@@ -234,7 +234,7 @@ func TestOnNewDeviceBobCanSeeButNotDecryptHistoryInPublicRoom(t *testing.T) {
 			csapiBob2 := tc.MustRegisterNewDevice(t, tc.Bob, "NEW_DEVICE")
 			tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 				User: csapiBob2,
-			}, func(bob2 api.Client) {
+			}, func(bob2 api.TestClient) {
 				time.Sleep(time.Second)             // let device keys propagate to alice
 				bob2.MustBackpaginate(t, roomID, 5) // ensure the older event is there
 				time.Sleep(time.Second)
@@ -265,7 +265,7 @@ func TestOnNewDeviceBobCanSeeButNotDecryptHistoryInPublicRoom(t *testing.T) {
 			// now bob logs in again
 			tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 				User: csapiBob2,
-			}, func(bob2 api.Client) {
+			}, func(bob2 api.TestClient) {
 				time.Sleep(time.Second) // let device keys propagate to alice
 				undecryptableEvent := bob2.MustGetEvent(t, roomID, evID)
 				must.Equal(t, undecryptableEvent.FailedToDecrypt, true, "bob's new device was able to decrypt a message sent after he had logged out")
@@ -282,7 +282,7 @@ func TestChangingDeviceAfterInviteReEncrypts(t *testing.T) {
 		// shared history visibility
 		roomID := tc.CreateNewEncryptedRoom(t, tc.Alice, cc.EncRoomOptions.PresetPublicChat())
 
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			// Alice invites Bob and then she sends an event
 			tc.Alice.MustInviteRoom(t, roomID, tc.Bob.UserID)
 			time.Sleep(time.Second) // let device keys propagate
@@ -293,7 +293,7 @@ func TestChangingDeviceAfterInviteReEncrypts(t *testing.T) {
 			csapiBob2 := tc.MustRegisterNewDevice(t, tc.Bob, "NEW_DEVICE")
 			tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 				User: csapiBob2,
-			}, func(bob2 api.Client) {
+			}, func(bob2 api.TestClient) {
 				time.Sleep(time.Second) // let device keys propagate
 				tc.Bob.MustJoinRoom(t, roomID, []string{clientTypeA.HS})
 
diff --git a/tests/one_time_keys_test.go b/tests/one_time_keys_test.go
index 6e5605a..6bac656 100644
--- a/tests/one_time_keys_test.go
+++ b/tests/one_time_keys_test.go
@@ -95,7 +95,7 @@ func TestFallbackKeyIsUsedIfOneTimeKeysRunOut(t *testing.T) {
 		// =================
 
 		// Upload OTKs and a fallback
-		tc.WithAliceBobAndCharlieSyncing(t, func(alice, bob, charlie api.Client) {
+		tc.WithAliceBobAndCharlieSyncing(t, func(alice, bob, charlie api.TestClient) {
 			// we need to send _something_ to cause /sync v2 to return a long poll response, as fallback
 			// keys don't wake up /sync v2. If we don't do this, rust SDK fails to realise it needs to upload a fallback
 			// key because SS doesn't tell it, because Synapse doesn't tell SS that the fallback key was used.
@@ -169,7 +169,7 @@ func TestFailedOneTimeKeyUploadRetries(t *testing.T) {
 			},
 			RequestCallback: callback.SendError(2, http.StatusGatewayTimeout),
 		}, func() {
-			tc.WithAliceSyncing(t, func(alice api.Client) {
+			tc.WithAliceSyncing(t, func(alice api.TestClient) {
 				tc.Bob.MustDo(t, "POST", []string{
 					"_matrix", "client", "v3", "keys", "claim",
 				}, client.WithJSONBody(t, map[string]any{
@@ -208,7 +208,7 @@ func TestFailedKeysClaimRetries(t *testing.T) {
 	Instance().ForEachClientType(t, func(t *testing.T, clientType api.ClientType) {
 		tc := Instance().CreateTestContext(t, clientType, clientType)
 		// both clients start syncing to upload OTKs
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			var stopPoking atomic.Bool
 			waiter := helpers.NewWaiter()
 			// make a room which will link the 2 users together when
diff --git a/tests/room_keys_test.go b/tests/room_keys_test.go
index c7284b2..baa5f80 100644
--- a/tests/room_keys_test.go
+++ b/tests/room_keys_test.go
@@ -57,7 +57,7 @@ func TestRoomKeyIsCycledOnDeviceLogout(t *testing.T) {
 			User: csapiAlice2,
 		})
 		defer alice2.Close(t)
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			alice2StopSyncing := alice2.MustStartSyncing(t)
 			alice.WaitUntilEventInRoom(t, roomID, api.CheckEventHasMembership(tc.Bob.UserID, "join")).Waitf(t, 5*time.Second, "alice did not see own join")
 			// check the room works
@@ -117,7 +117,7 @@ func TestRoomKeyIsCycledAfterEnoughMessages(t *testing.T) {
 		)
 		tc.Bob.MustJoinRoom(t, roomID, []string{clientTypeA.HS})
 
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			// And some messages were sent, but not enough to trigger resending
 			for i := 0; i < 4; i++ {
 				wantMsgBody := fmt.Sprintf("Before we hit the threshold %d", i)
@@ -191,7 +191,7 @@ func TestRoomKeyIsCycledAfterEnoughTime(t *testing.T) {
 		)
 		tc.Bob.MustJoinRoom(t, roomID, []string{clientTypeA.HS})
 
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			// Before we start, ensure some keys have already been sent, so we
 			// don't get a false positive.
 			wantMsgBody := "Before we start"
@@ -226,7 +226,7 @@ func TestRoomKeyIsCycledOnMemberLeaving(t *testing.T) {
 	Instance().ClientTypeMatrix(t, func(t *testing.T, clientTypeA, clientTypeB api.ClientType) {
 		tc := Instance().CreateTestContext(t, clientTypeA, clientTypeB, clientTypeB)
 		// Alice, Bob and Charlie are in a room.
-		tc.WithAliceBobAndCharlieSyncing(t, func(alice, bob, charlie api.Client) {
+		tc.WithAliceBobAndCharlieSyncing(t, func(alice, bob, charlie api.TestClient) {
 			// do setup code after all clients are syncing to ensure that if Alice asks for Charlie's keys on receipt of the
 			// join event, then Charlie has already uploaded keys.
 			roomID := tc.CreateNewEncryptedRoom(
@@ -281,7 +281,7 @@ func TestRoomKeyIsNotCycled(t *testing.T) {
 		tc.Bob.MustJoinRoom(t, roomID, []string{clientTypeA.HS})
 
 		// Alice, Bob are in a room.
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			// check the room works
 			wantMsgBody := "Test Message"
 			waiter := bob.WaitUntilEventInRoom(t, roomID, api.CheckEventHasBody(wantMsgBody))
@@ -407,7 +407,7 @@ func testRoomKeyIsNotCycledOnClientRestartRust(t *testing.T, clientType api.Clie
 
 	tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 		User: tc.Bob,
-	}, func(bob api.Client) {
+	}, func(bob api.TestClient) {
 		wantMsgBody := "test from another process"
 		// send a message as Alice in a different process
 		tc.WithClientSyncing(t, &cc.ClientCreationRequest{
@@ -416,7 +416,7 @@ func testRoomKeyIsNotCycledOnClientRestartRust(t *testing.T, clientType api.Clie
 				PersistentStorage: true,
 			},
 			Multiprocess: true,
-		}, func(remoteAlice api.Client) {
+		}, func(remoteAlice api.TestClient) {
 			eventID := remoteAlice.SendMessage(t, roomID, wantMsgBody)
 			waiter := remoteAlice.WaitUntilEventInRoom(t, roomID, api.CheckEventHasEventID(eventID))
 			waiter.Waitf(t, 5*time.Second, "client did not see event %s", eventID)
@@ -480,7 +480,7 @@ func testRoomKeyIsNotCycledOnClientRestartJS(t *testing.T, clientType api.Client
 	// no alice.close here as we'll close it in the test mid-way
 	tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 		User: tc.Bob,
-	}, func(bob api.Client) {
+	}, func(bob api.TestClient) {
 		// check the room works
 		wantMsgBody := "Test Message"
 		waiter := bob.WaitUntilEventInRoom(t, roomID, api.CheckEventHasBody(wantMsgBody))
@@ -496,7 +496,7 @@ func testRoomKeyIsNotCycledOnClientRestartJS(t *testing.T, clientType api.Client
 			tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 				User: tc.Alice,
 				Opts: alice.Opts(),
-			}, func(alice api.Client) {
+			}, func(alice api.TestClient) {
 				// now send another message from Alice, who should NOT send another new room key
 				wantMsgBody = "Another Test Message"
 				waiter = bob.WaitUntilEventInRoom(t, roomID, api.CheckEventHasBody(wantMsgBody))
diff --git a/tests/rust/notification_test.go b/tests/rust/notification_test.go
index f791322..47bf815 100644
--- a/tests/rust/notification_test.go
+++ b/tests/rust/notification_test.go
@@ -118,7 +118,7 @@ func TestNSEReceiveForNonPreKeyMessage(t *testing.T) {
 	// Bob sends a message to alice
 	tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 		User: tc.Bob,
-	}, func(bob api.Client) {
+	}, func(bob api.TestClient) {
 		// let bob realise alice exists and claims keys
 		time.Sleep(time.Second)
 		// Send a message as Bob, this will contain ensure an Olm session is set up already before we do NSE work
@@ -175,7 +175,7 @@ func TestMultiprocessNSE(t *testing.T) {
 	// Bob sends a message to alice
 	tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 		User: tc.Bob,
-	}, func(bob api.Client) {
+	}, func(bob api.TestClient) {
 		// let bob realise alice exists and claims keys
 		time.Sleep(time.Second)
 		for i := 0; i < numPreBackgroundMsgs; i++ {
@@ -336,7 +336,7 @@ func TestMultiprocessNSEBackupKeyMacError(t *testing.T) {
 	// Bob sends a message to alice
 	tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 		User: tc.Bob,
-	}, func(bob api.Client) {
+	}, func(bob api.TestClient) {
 		// let bob realise alice exists and claims keys
 		time.Sleep(time.Second)
 
@@ -452,7 +452,7 @@ func TestMultiprocessNSEOlmSessionWedge(t *testing.T) {
 	// Bob sends a message to alice
 	tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 		User: tc.Bob,
-	}, func(bob api.Client) {
+	}, func(bob api.TestClient) {
 		// let bob realise alice exists and claims keys
 		time.Sleep(time.Second)
 		msg := "pre message"
@@ -599,7 +599,7 @@ func TestNotificationClientDupeOTKUpload(t *testing.T) {
 		// The main app will see this in /sync and then try to upload another OTK, which we will tarpit.
 		tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 			User: tc.Bob,
-		}, func(bob api.Client) {
+		}, func(bob api.TestClient) {
 			eventID := bob.SendMessage(t, roomID, "Hello world!")
 			// create a NotificationClient in the same process to fetch this "push notification".
 			// It might make the NotificationClient upload a OTK as it would have seen 1 has been used.
@@ -648,7 +648,7 @@ func TestMultiprocessInitialE2EESyncDoesntDropDeviceListUpdates(t *testing.T) {
 	// Bob sends a message to Alice
 	tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 		User: tc.Alice,
-	}, func(alice api.Client) {
+	}, func(alice api.TestClient) {
 		// ensure bob has queried keys from alice by sending a message.
 		msg := "pre message"
 		bob.SendMessage(t, roomID, msg)
@@ -700,7 +700,7 @@ func TestMultiprocessInitialE2EESyncDoesntDropDeviceListUpdates(t *testing.T) {
 		csapiAlice2 := tc.MustRegisterNewDevice(t, tc.Alice, "NEW_DEVICE")
 		tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 			User: csapiAlice2,
-		}, func(alice2 api.Client) {
+		}, func(alice2 api.TestClient) {
 			// wait for device keys to sync up
 			time.Sleep(time.Second)
 			// alice[1] sends a message, this is unimportant other than to grab the event ID for the push process
@@ -750,7 +750,7 @@ func bobSendsMessage(t *testing.T, tc *cc.TestContext, roomID, text string, msgs
 	pushNotifEventID := ""
 	tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 		User: tc.Bob,
-	}, func(bob api.Client) {
+	}, func(bob api.TestClient) {
 		for i := 0; i < msgsBefore; i++ {
 			bob.SendMessage(t, roomID, fmt.Sprintf("msg before %d", i))
 		}
diff --git a/tests/to_device_test.go b/tests/to_device_test.go
index 102b6d3..56a852d 100644
--- a/tests/to_device_test.go
+++ b/tests/to_device_test.go
@@ -22,7 +22,7 @@ func TestClientRetriesSendToDevice(t *testing.T) {
 		tc := Instance().CreateTestContext(t, clientTypeA, clientTypeB)
 		roomID := tc.CreateNewEncryptedRoom(t, tc.Alice, cc.EncRoomOptions.PresetPublicChat())
 		tc.Bob.MustJoinRoom(t, roomID, []string{clientTypeA.HS})
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			// lets device keys be exchanged
 			time.Sleep(time.Second)
 
@@ -85,7 +85,7 @@ func TestUnprocessedToDeviceMessagesArentLostOnRestart(t *testing.T) {
 				PersistentStorage: true,
 			},
 		})
-		tc.WithAliceSyncing(t, func(alice api.Client) {
+		tc.WithAliceSyncing(t, func(alice api.TestClient) {
 			// we will close this in the test, no defer
 			bobStopSyncing := bob.MustStartSyncing(t)
 			// check the room works
@@ -178,7 +178,7 @@ func testUnprocessedToDeviceMessagesArentLostOnRestartRust(t *testing.T, tc *cc.
 			Opts: api.ClientCreationOpts{
 				PersistentStorage: true,
 			},
-		}, func(bob api.Client) {
+		}, func(bob api.TestClient) {
 			// we can't rely on MustStartSyncing returning to know that the room key has been received, as
 			// in rust we just wait for RoomListLoadingStateLoaded which is a separate connection to the
 			// encryption loop.
@@ -242,7 +242,7 @@ func testUnprocessedToDeviceMessagesArentLostOnRestartJS(t *testing.T, tc *cc.Te
 			Opts: api.ClientCreationOpts{
 				PersistentStorage: true,
 			},
-		}, func(bob api.Client) {
+		}, func(bob api.TestClient) {
 			// include a grace period like rust, no specific reason beyond consistency.
 			time.Sleep(time.Second)
 			ev := bob.MustGetEvent(t, roomID, eventID)
@@ -282,7 +282,7 @@ func TestToDeviceMessagesAreBatched(t *testing.T) {
 			clientUnderTest.Close(t)
 		}
 		waiter := helpers.NewWaiter()
-		tc.WithAliceSyncing(t, func(alice api.Client) {
+		tc.WithAliceSyncing(t, func(alice api.TestClient) {
 			// intercept /sendToDevice and check we are sending 100 messages per request
 			tc.Deployment.MITM().Configure(t).WithIntercept(mitm.InterceptOpts{
 				Filter: mitm.FilterParams{
@@ -345,7 +345,7 @@ func TestToDeviceMessagesArentLostWhenKeysQueryFails(t *testing.T) {
 		// get a normal E2EE room set up
 		roomID := tc.CreateNewEncryptedRoom(t, tc.Alice, cc.EncRoomOptions.Invite([]string{tc.Bob.UserID}))
 		tc.Bob.MustJoinRoom(t, roomID, []string{clientType.HS})
-		tc.WithAliceAndBobSyncing(t, func(alice, bob api.Client) {
+		tc.WithAliceAndBobSyncing(t, func(alice, bob api.TestClient) {
 			msg := "hello world"
 			msg2 := "new device message from alice"
 			alice.SendMessage(t, roomID, msg)
@@ -370,7 +370,7 @@ func TestToDeviceMessagesArentLostWhenKeysQueryFails(t *testing.T) {
 				csapiAlice2 := tc.MustRegisterNewDevice(t, tc.Alice, "OTHER_DEVICE")
 				tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 					User: csapiAlice2,
-				}, func(alice2 api.Client) {
+				}, func(alice2 api.TestClient) {
 					// we don't know how long it will take for the device list update to be processed, so wait 1s
 					time.Sleep(time.Second)
 
@@ -429,7 +429,7 @@ func TestToDeviceMessagesAreProcessedInOrder(t *testing.T) {
 			ID   string
 			Body string
 		}{}
-		tc.WithAliceSyncing(t, func(alice api.Client) {
+		tc.WithAliceSyncing(t, func(alice api.TestClient) {
 			callbackFn := func(cd callback.Data) *callback.Response {
 				// try v2 sync then SS
 				toDeviceEvents := gjson.ParseBytes(cd.ResponseBody).Get("to_device.events").Array()
@@ -469,7 +469,7 @@ func TestToDeviceMessagesAreProcessedInOrder(t *testing.T) {
 					creationReqs[i].User.MustJoinRoom(t, roomID, []string{clientType.HS})
 				}
 				// send 30 messages as each user (interleaved)
-				tc.WithClientsSyncing(t, creationReqs, func(clients []api.Client) {
+				tc.WithClientsSyncing(t, creationReqs, func(clients []api.TestClient) {
 					for i := 0; i < numMsgsPerClient; i++ {
 						for _, c := range clients {
 							body := fmt.Sprintf("Message %d", i+1)
diff --git a/tests/verification_test.go b/tests/verification_test.go
index d437795..e1d6f74 100644
--- a/tests/verification_test.go
+++ b/tests/verification_test.go
@@ -67,13 +67,13 @@ func TestVerificationSAS(t *testing.T) {
 			ClientType: verifieeClientType,
 		}
 
-		tc.WithAliceSyncing(t, func(verifier api.Client) {
+		tc.WithAliceSyncing(t, func(verifier api.TestClient) {
 			tc.WithClientSyncing(t, &cc.ClientCreationRequest{
 				User: verifieeUser,
 				Opts: api.ClientCreationOpts{
 					DeviceID: "OTHER_DEVICE",
 				},
-			}, func(verifiee api.Client) {
+			}, func(verifiee api.TestClient) {
 				status := &verificationStatus{
 					mu: &sync.Mutex{},
 				}