diff --git a/src/common/lib/transport/connectionmanager.ts b/src/common/lib/transport/connectionmanager.ts
index cc6b1d6637..5e5845bcb5 100644
--- a/src/common/lib/transport/connectionmanager.ts
+++ b/src/common/lib/transport/connectionmanager.ts
@@ -99,8 +99,6 @@ function decodeRecoveryKey(recoveryKey: NormalisedClientOptions['recover']): Rec
   }
 }
 
-const supportedTransports: Partial<Record<TransportName, TransportCtor>> = {};
-
 export class TransportParams {
   options: NormalisedClientOptions;
   host: string | null;
@@ -190,6 +188,7 @@ type ConnectionState = {
 };
 
 class ConnectionManager extends EventEmitter {
+  supportedTransports: Partial<Record<TransportName, TransportCtor>> = {};
   realtime: BaseRealtime;
   options: NormalisedClientOptions;
   states: Record<string, ConnectionState>;
@@ -228,7 +227,7 @@ class ConnectionManager extends EventEmitter {
 
   constructor(realtime: BaseRealtime, options: NormalisedClientOptions) {
     super();
-    ConnectionManager.initTransports();
+    this.initTransports();
     this.realtime = realtime;
     this.options = options;
     const timeouts = options.timeouts;
@@ -305,10 +304,7 @@ class ConnectionManager extends EventEmitter {
     this.connectionStateTtl = timeouts.connectionStateTtl;
     this.maxIdleInterval = null;
 
-    this.transports = Utils.intersect(
-      options.transports || Defaults.defaultTransports,
-      ConnectionManager.supportedTransports
-    );
+    this.transports = Utils.intersect(options.transports || Defaults.defaultTransports, this.supportedTransports);
     /* baseTransports selects the leftmost transport in the Defaults.baseTransportOrder list
      * that's both requested and supported. */
     this.baseTransport = Utils.intersect(Defaults.baseTransportOrder, this.transports)[0];
@@ -404,18 +400,25 @@ class ConnectionManager extends EventEmitter {
    * transport management
    *********************/
 
+  // Used by tests
   static get supportedTransports() {
-    return supportedTransports;
+    const storage: TransportStorage = { supportedTransports: {} };
+    this.initTransports(storage);
+    return storage.supportedTransports;
   }
 
-  static initTransports() {
-    WebSocketTransport(ConnectionManager);
+  private static initTransports(storage: TransportStorage) {
+    WebSocketTransport(storage);
     Utils.arrForEach(Platform.Transports.order, function (transportName) {
       const initFn = Platform.Transports.implementations[transportName]!;
       initFn(ConnectionManager);
     });
   }
 
+  initTransports() {
+    ConnectionManager.initTransports(this);
+  }
+
   createTransportParams(host: string | null, mode: string): TransportParams {
     return new TransportParams(this.options, host, mode, this.connectionKey);
   }
@@ -486,7 +489,7 @@ class ConnectionManager extends EventEmitter {
     Logger.logAction(Logger.LOG_MICRO, 'ConnectionManager.tryATransport()', 'trying ' + candidate);
 
     Transport.tryConnect(
-      ConnectionManager.supportedTransports[candidate]!,
+      this.supportedTransports[candidate]!,
       this,
       this.realtime.auth,
       transportParams,
@@ -2171,4 +2174,8 @@ class ConnectionManager extends EventEmitter {
 
 export default ConnectionManager;
 
-export type TransportInitialiser = (connectionManager: typeof ConnectionManager) => typeof Transport;
+export interface TransportStorage {
+  supportedTransports: Partial<Record<TransportName, TransportCtor>>;
+}
+
+export type TransportInitialiser = (transportStorage: TransportStorage) => typeof Transport;
diff --git a/src/common/lib/transport/websockettransport.ts b/src/common/lib/transport/websockettransport.ts
index 2324fc3021..cef583bd59 100644
--- a/src/common/lib/transport/websockettransport.ts
+++ b/src/common/lib/transport/websockettransport.ts
@@ -6,7 +6,7 @@ import Logger from '../util/logger';
 import ProtocolMessage from '../types/protocolmessage';
 import ErrorInfo from '../types/errorinfo';
 import NodeWebSocket from 'ws';
-import ConnectionManager, { TransportParams } from './connectionmanager';
+import ConnectionManager, { TransportParams, TransportStorage } from './connectionmanager';
 import Auth from '../client/auth';
 import { TransportNames } from 'common/constants/TransportName';
 
@@ -196,8 +196,8 @@ class WebSocketTransport extends Transport {
   }
 }
 
-function initialiseTransport(connectionManager: typeof ConnectionManager): typeof WebSocketTransport {
-  if (WebSocketTransport.isAvailable()) connectionManager.supportedTransports[shortName] = WebSocketTransport;
+function initialiseTransport(transportStorage: TransportStorage): typeof WebSocketTransport {
+  if (WebSocketTransport.isAvailable()) transportStorage.supportedTransports[shortName] = WebSocketTransport;
 
   return WebSocketTransport;
 }
diff --git a/src/platform/nodejs/lib/transport/nodecomettransport.d.ts b/src/platform/nodejs/lib/transport/nodecomettransport.d.ts
index 9067155ab9..f90fa468b0 100644
--- a/src/platform/nodejs/lib/transport/nodecomettransport.d.ts
+++ b/src/platform/nodejs/lib/transport/nodecomettransport.d.ts
@@ -1,5 +1,5 @@
-import ConnectionManager from '../../../../common/lib/transport/connectionmanager';
+import { TransportStorage } from '../../../../common/lib/transport/connectionmanager';
 import Transport from '../../../../common/lib/transport/transport';
 
-declare function initialiseNodeCometTransport(connectionManager: typeof ConnectionManager): typeof Transport;
+declare function initialiseNodeCometTransport(transportStorage: TransportStorage): typeof Transport;
 export default initialiseNodeCometTransport;
diff --git a/src/platform/nodejs/lib/transport/nodecomettransport.js b/src/platform/nodejs/lib/transport/nodecomettransport.js
index 6e6655bb0d..9a1c29411d 100644
--- a/src/platform/nodejs/lib/transport/nodecomettransport.js
+++ b/src/platform/nodejs/lib/transport/nodecomettransport.js
@@ -12,7 +12,7 @@ import url from 'url';
 import util from 'util';
 import { TransportNames } from '../../../../common/constants/TransportName';
 
-var NodeCometTransport = function (connectionManager) {
+var NodeCometTransport = function (transportStorage) {
   var noop = function () {};
   var shortName = TransportNames.Comet;
 
@@ -32,7 +32,7 @@ var NodeCometTransport = function (connectionManager) {
   NodeCometTransport.isAvailable = function () {
     return true;
   };
-  connectionManager.supportedTransports[shortName] = NodeCometTransport;
+  transportStorage.supportedTransports[shortName] = NodeCometTransport;
 
   NodeCometTransport.prototype.toString = function () {
     return (
diff --git a/src/platform/web/lib/transport/xhrpollingtransport.ts b/src/platform/web/lib/transport/xhrpollingtransport.ts
index c063397198..4d3b2110d3 100644
--- a/src/platform/web/lib/transport/xhrpollingtransport.ts
+++ b/src/platform/web/lib/transport/xhrpollingtransport.ts
@@ -1,7 +1,7 @@
 import Platform from '../../../../common/platform';
 import CometTransport from '../../../../common/lib/transport/comettransport';
 import XHRRequest from './xhrrequest';
-import ConnectionManager, { TransportParams } from 'common/lib/transport/connectionmanager';
+import ConnectionManager, { TransportParams, TransportStorage } from 'common/lib/transport/connectionmanager';
 import Auth from 'common/lib/client/auth';
 import { RequestParams } from 'common/types/http';
 import { TransportNames } from 'common/constants/TransportName';
@@ -34,8 +34,8 @@ class XHRPollingTransport extends CometTransport {
   }
 }
 
-function initialiseTransport(connectionManager: typeof ConnectionManager): typeof XHRPollingTransport {
-  if (XHRPollingTransport.isAvailable()) connectionManager.supportedTransports[shortName] = XHRPollingTransport;
+function initialiseTransport(transportStorage: TransportStorage): typeof XHRPollingTransport {
+  if (XHRPollingTransport.isAvailable()) transportStorage.supportedTransports[shortName] = XHRPollingTransport;
 
   return XHRPollingTransport;
 }
diff --git a/src/platform/web/lib/transport/xhrstreamingtransport.ts b/src/platform/web/lib/transport/xhrstreamingtransport.ts
index 57cf30e7b7..9ef8631fec 100644
--- a/src/platform/web/lib/transport/xhrstreamingtransport.ts
+++ b/src/platform/web/lib/transport/xhrstreamingtransport.ts
@@ -1,7 +1,7 @@
 import CometTransport from '../../../../common/lib/transport/comettransport';
 import Platform from '../../../../common/platform';
 import XHRRequest from './xhrrequest';
-import ConnectionManager, { TransportParams } from 'common/lib/transport/connectionmanager';
+import ConnectionManager, { TransportParams, TransportStorage } from 'common/lib/transport/connectionmanager';
 import Auth from 'common/lib/client/auth';
 import { RequestParams } from 'common/types/http';
 import { TransportNames } from 'common/constants/TransportName';
@@ -32,8 +32,8 @@ class XHRStreamingTransport extends CometTransport {
   }
 }
 
-function initialiseTransport(connectionManager: typeof ConnectionManager): typeof XHRStreamingTransport {
-  if (XHRStreamingTransport.isAvailable()) connectionManager.supportedTransports[shortName] = XHRStreamingTransport;
+function initialiseTransport(transportStorage: TransportStorage): typeof XHRStreamingTransport {
+  if (XHRStreamingTransport.isAvailable()) transportStorage.supportedTransports[shortName] = XHRStreamingTransport;
 
   return XHRStreamingTransport;
 }
diff --git a/test/common/modules/shared_helper.js b/test/common/modules/shared_helper.js
index 58ad02989e..8c3eb6c16d 100644
--- a/test/common/modules/shared_helper.js
+++ b/test/common/modules/shared_helper.js
@@ -14,7 +14,6 @@ define([
   var platform = clientModule.Ably.Realtime.Platform;
   var BufferUtils = platform.BufferUtils;
   var expect = chai.expect;
-  clientModule.Ably.Realtime.ConnectionManager.initTransports();
   var availableTransports = utils.keysArray(clientModule.Ably.Realtime.ConnectionManager.supportedTransports),
     bestTransport = availableTransports[0],
     /* IANA reserved; requests to it will hang forever */