Add test for sticky header functionality

Co-authored-by: alexr00 <38270282+alexr00@users.noreply.github.com>

Author: Copilot

webviews/editorWebview/test/overview.test.tsx

@@ -0,0 +1,57 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { default as assert } from 'assert';
+import * as React from 'react';
+import { cleanup, render } from 'react-testing-library';
+import { createSandbox, SinonSandbox } from 'sinon';
+
+import { PRContext, default as PullRequestContext } from '../../common/context';
+import { Overview } from '../overview';
+import { PullRequestBuilder } from './builder/pullRequest';
+
+describe('Overview', function () {
+	let sinon: SinonSandbox;
+
+	beforeEach(function () {
+		sinon = createSandbox();
+	});
+
+	afterEach(function () {
+		cleanup();
+		sinon.restore();
+	});
+
+	it('renders the PR header with title', function () {
+		const pr = new PullRequestBuilder().build();
+		const context = new PRContext(pr);
+
+		const out = render(
+			<PullRequestContext.Provider value={context}>
+				<Overview {...pr} />
+			</PullRequestContext.Provider>,
+		);
+
+		assert(out.container.querySelector('.title'));
+		assert(out.container.querySelector('.overview-title'));
+	});
+
+	it('applies sticky class when scrolled', function () {
+		const pr = new PullRequestBuilder().build();
+		const context = new PRContext(pr);
+
+		const out = render(
+			<PullRequestContext.Provider value={context}>
+				<Overview {...pr} />
+			</PullRequestContext.Provider>,
+		);
+
+		const titleElement = out.container.querySelector('.title');
+		assert(titleElement);
+
+		// Initial state should not have sticky class
+		assert(!titleElement.classList.contains('sticky'));
+	});
+});