Smoke test for multi root (#31059)

* wip

* fix for windows

* add some tests

* only run multi root test on windows

* fix bug with opening files into a workspace that opens (enables smoke test)

* document how to run against out of source

* enable test for all OS

test/smoke/src/tests/multiroot.ts

@@ -0,0 +1,42 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as assert from 'assert';
+
+import { SpectronApplication, LATEST_PATH, CODE_WORKSPACE_PATH } from "../spectron/application";
+import { CommonActions } from '../areas/common';
+
+let app: SpectronApplication;
+let common: CommonActions;
+
+export function testMultiRoot() {
+	context('Multi Root', () => {
+
+		beforeEach(async function () {
+			app = new SpectronApplication(LATEST_PATH, this.currentTest.fullTitle(), (this.currentTest as any).currentRetry(), [CODE_WORKSPACE_PATH]);
+			common = new CommonActions(app);
+
+			return await app.start();
+		});
+
+		afterEach(async function () {
+			return await app.stop();
+		});
+
+		it('shows results from all folders', async function () {
+			await common.openQuickOpen();
+			await common.type('*.*');
+			await app.wait();
+			const elCount = await common.getQuickOpenElements();
+			assert.equal(elCount, 6);
+		});
+
+		it('shows workspace name in title', async function () {
+			await app.wait();
+			const title = await common.getWindowTitle();
+			assert.ok(title.indexOf('smoketest (Workspace)') >= 0);
+		});
+	});
+}