Warn on async suites (#188378)

Part of #187718

.eslintplugin/code-no-test-async-suite.ts

@@ -0,0 +1,33 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { TSESTree } from '@typescript-eslint/experimental-utils';
+import * as eslint from 'eslint';
+
+function isCallExpression(node: TSESTree.Node): node is TSESTree.CallExpression {
+	return node.type === 'CallExpression';
+}
+
+function isFunctionExpression(node: TSESTree.Node): node is TSESTree.FunctionExpression {
+	return node.type.includes('FunctionExpression');
+}
+
+export = new class NoAsyncSuite implements eslint.Rule.RuleModule {
+
+	create(context: eslint.Rule.RuleContext): eslint.Rule.RuleListener {
+		function hasAsyncSuite(node: any) {
+			if (isCallExpression(node) && node.arguments.length >= 2 && isFunctionExpression(node.arguments[1]) && node.arguments[1].async) {
+				return context.report({
+					node: node as any,
+					message: 'suite factory function should never be async'
+				});
+			}
+		}
+
+		return {
+			['CallExpression[callee.name=/suite$/][arguments]']: hasAsyncSuite,
+		};
+	}
+};

.eslintrc.json

@@ -120,6 +120,7 @@
 			],
 			"rules": {
 				"local/code-no-test-only": "error",
+				"local/code-no-test-async-suite": "warn",
 				"local/code-no-unexternalized-strings": "off"
 			}
 		},