diff --git a/cspell.json b/cspell.json
index 0250b7d..e718955 100644
--- a/cspell.json
+++ b/cspell.json
@@ -39,6 +39,7 @@
     "coreutils",
     "csstree",
     "deepnote",
+    "exenv",
     "ipynb",
     "Jakubowski",
     "jlpm",
diff --git a/jest.config.js b/jest.config.js
index 248d8cf..db456ae 100644
--- a/jest.config.js
+++ b/jest.config.js
@@ -2,8 +2,9 @@ const jestJupyterLab = require('@jupyterlab/testutils/lib/jest-config');
 
 const esModules = [
   '@codemirror',
-  '@jupyter/ydoc',
-  '@jupyterlab/',
+  '@jupyter',
+  '@microsoft',
+  'exenv-es6',
   'lib0',
   'nanoid',
   'vscode-ws-jsonrpc',
diff --git a/src/__tests__/NotebookPicker.spec.ts b/src/__tests__/NotebookPicker.spec.ts
new file mode 100644
index 0000000..4708c5b
--- /dev/null
+++ b/src/__tests__/NotebookPicker.spec.ts
@@ -0,0 +1,111 @@
+// Copyright (c) Deepnote
+// Distributed under the terms of the Modified BSD License.
+
+import { NotebookPicker } from '../../src/components/NotebookPicker';
+import { framePromise } from '@jupyterlab/testing';
+import { NotebookPanel } from '@jupyterlab/notebook';
+import { INotebookModel } from '@jupyterlab/notebook';
+import { Widget } from '@lumino/widgets';
+import { simulate } from 'simulate-event';
+
+describe('NotebookPicker', () => {
+  let panel: NotebookPanel;
+  let model: INotebookModel;
+
+  beforeEach(async () => {
+    // Mock model + metadata
+    model = {
+      fromJSON: jest.fn(),
+      get cells() {
+        return [];
+      },
+      dirty: true
+    } as any;
+
+    panel = {
+      context: {
+        ready: Promise.resolve(),
+        model: {
+          getMetadata: jest.fn().mockReturnValue({
+            notebooks: {
+              nb1: { id: 'nb1', name: 'nb1', cells: [{ source: 'code' }] },
+              nb2: { id: 'nb2', name: 'nb2', cells: [] }
+            },
+            notebook_names: ['nb1', 'nb2']
+          })
+        }
+      },
+      model
+    } as any;
+
+    // Attach to DOM
+    const widget = new NotebookPicker(panel);
+    // Override onAfterAttach to avoid errors from this.parent being null
+    (widget as any).onAfterAttach = jest.fn();
+    Widget.attach(widget, document.body);
+    await framePromise();
+  });
+
+  afterEach(() => {
+    document.body.innerHTML = '';
+    jest.restoreAllMocks();
+  });
+
+  it('should render a select element', async () => {
+    await framePromise(); // wait for rendering
+    const select = document.querySelector('select') as HTMLSelectElement;
+    expect(select).not.toBeNull();
+    expect(select.options.length).toBe(2);
+    expect(select.options[0] && select.options[0].value).toBe('nb1');
+  });
+
+  it('should call fromJSON when selecting a notebook', async () => {
+    const select = document.querySelector('select') as HTMLSelectElement;
+    simulate(select, 'change', { target: { value: 'nb2' } });
+    await framePromise();
+    expect(model.fromJSON).toHaveBeenCalledWith(
+      expect.objectContaining({
+        cells: expect.any(Array),
+        metadata: expect.objectContaining({
+          deepnote: expect.objectContaining({
+            notebooks: expect.any(Object)
+          })
+        })
+      })
+    );
+  });
+
+  it('should not call fromJSON if selected notebook is invalid', async () => {
+    const getMetadata = panel.context.model.getMetadata as jest.Mock;
+    getMetadata.mockReturnValue({ notebooks: {}, notebook_names: [] });
+
+    const select = document.querySelector('select') as HTMLSelectElement;
+    simulate(select, 'change', { target: { value: 'nonexistent' } });
+    await framePromise();
+    expect(model.fromJSON).not.toHaveBeenCalled();
+  });
+
+  it('should update UI after selection', async () => {
+    const select = document.querySelector('select') as HTMLSelectElement;
+    select.value = 'nb2';
+    simulate(select, 'change');
+    await framePromise();
+    expect(select.value).toBe('nb2');
+  });
+
+  it('should handle empty metadata gracefully', async () => {
+    const getMetadata = panel.context.model.getMetadata as jest.Mock;
+    getMetadata.mockReturnValue({ notebooks: {}, notebook_names: [] });
+
+    document.body.innerHTML = '';
+    const widget = new NotebookPicker(panel);
+    // Override onAfterAttach to avoid errors from this.parent being null
+    (widget as any).onAfterAttach = jest.fn();
+    Widget.attach(widget, document.body);
+    await framePromise();
+
+    const select = document.querySelector('select') as HTMLSelectElement;
+    expect(select.options.length).toBeGreaterThanOrEqual(1);
+    expect(select.options[0] && select.options[0].value).toBe('-');
+  });
+});
diff --git a/src/components/NotebookPicker.tsx b/src/components/NotebookPicker.tsx
index d683106..1dbb941 100644
--- a/src/components/NotebookPicker.tsx
+++ b/src/components/NotebookPicker.tsx
@@ -3,6 +3,8 @@ import { ReactWidget } from '@jupyterlab/apputils';
 import { NotebookPanel } from '@jupyterlab/notebook';
 import { HTMLSelect } from '@jupyterlab/ui-components';
 import { deepnoteMetadataSchema } from '../types';
+import { Widget } from '@lumino/widgets';
+import { Message, MessageLoop } from '@lumino/messaging';
 
 export class NotebookPicker extends ReactWidget {
   private selected: string | null = null;
@@ -63,6 +65,13 @@ export class NotebookPicker extends ReactWidget {
     this.update();
   };
 
+  protected onAfterAttach(msg: Message): void {
+    super.onAfterAttach(msg);
+    requestAnimationFrame(() => {
+      MessageLoop.sendMessage(this.parent!, Widget.ResizeMessage.UnknownSize);
+    });
+  }
+
   render(): JSX.Element {
     const deepnoteMetadata = this.panel.context.model.getMetadata('deepnote');
 
@@ -81,7 +90,7 @@ export class NotebookPicker extends ReactWidget {
         aria-label="Select active notebook"
         title="Select active notebook"
         style={{
-          maxWidth: '120px',
+          width: '120px',
           textOverflow: 'ellipsis',
           whiteSpace: 'nowrap',
           overflow: 'hidden'