Fixing bug where templates may get mapped before loaded from their files (#10111)

* Fixing potential bad order of template loading and map construction

* Fixing bug where templates get mapped before loaded from file

* Parallelizing loading templates from file

extensions/sql-database-projects/src/test/templates.test.ts

@@ -0,0 +1,39 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as should from 'should';
+import * as path from 'path';
+import * as templates from '../templates/templates';
+import { shouldThrowSpecificError } from './testUtils';
+
+describe('Templates: loading templates from disk', function (): void {
+	beforeEach(() => {
+		templates.reset();
+	});
+
+	it('Should throw error when attempting to use templates before loaded from file', async function (): Promise<void> {
+		shouldThrowSpecificError(() => templates.projectScriptTypeMap(), 'Templates must be loaded from file before attempting to use.');
+		shouldThrowSpecificError(() => templates.projectScriptTypes(), 'Templates must be loaded from file before attempting to use.');
+	});
+
+	it('Should load all templates from files', async function (): Promise<void> {
+		await templates.loadTemplates(path.join(__dirname, '..', '..', 'resources', 'templates'));
+
+		// check expected counts
+
+		const numScriptObjectTypes = 4;
+
+		should(templates.projectScriptTypes().length).equal(numScriptObjectTypes);
+		should(Object.keys(templates.projectScriptTypes()).length).equal(numScriptObjectTypes);
+
+		// check everything has a value
+
+		should(templates.newSqlProjectTemplate).not.equal(undefined);
+
+		for (const obj of templates.projectScriptTypes()) {
+			should(obj.templateScript).not.equal(undefined);
+		}
+	});
+});