Add multiple tabs test

Author: stevensJourney

packages/web/tests/mocks/MockWebRemote.ts

@@ -0,0 +1,56 @@
+import {
+  AbstractRemote,
+  AbstractRemoteOptions,
+  BSONImplementation,
+  DEFAULT_REMOTE_LOGGER,
+  FetchImplementation,
+  FetchImplementationProvider,
+  ILogger,
+  RemoteConnector
+} from '@powersync/common';
+
+/**
+ * Mock WebRemote that throws 401 Unauthorized errors for all HTTP requests.
+ * Used for testing error handling in the shared sync worker.
+ * Other tests may override this for managed streams.
+ */
+class MockFetchProvider extends FetchImplementationProvider {
+  getFetch(): FetchImplementation {
+    // Return a mock fetch that always returns 401
+    return async (input: RequestInfo | URL, init?: RequestInit): Promise<Response> => {
+      const response = new Response(null, {
+        status: 401,
+        statusText: 'Unauthorized'
+      });
+      return response;
+    };
+  }
+}
+
+export class WebRemote extends AbstractRemote {
+  private _bson: BSONImplementation | undefined;
+
+  constructor(
+    protected connector: RemoteConnector,
+    protected logger: ILogger = DEFAULT_REMOTE_LOGGER,
+    options?: Partial<AbstractRemoteOptions>
+  ) {
+    super(connector, logger, {
+      ...(options ?? {}),
+      fetchImplementation: options?.fetchImplementation ?? new MockFetchProvider()
+    });
+  }
+
+  getUserAgent(): string {
+    return 'powersync-web-mock';
+  }
+
+  async getBSON(): Promise<BSONImplementation> {
+    if (this._bson) {
+      return this._bson;
+    }
+    const { BSON } = await import('bson');
+    this._bson = BSON;
+    return this._bson;
+  }
+}