Update: More detailed assert message for rule-tester (#9769)

* Update: More detailed assert message for rule-tester

* [squash]add try/finally block

* [squash]append message instead of overwriting it

* [squash]add parentheses surrounding error message

lib/testers/rule-tester.js

@@ -131,13 +131,31 @@ const DESCRIBE = Symbol("describe");
 const IT = Symbol("it");
 
 /**
- * This is `it` or `describe` if those don't exist.
+ * This is `it` default handler if `it` don't exist.
  * @this {Mocha}
  * @param {string} text - The description of the test case.
  * @param {Function} method - The logic of the test case.
  * @returns {any} Returned value of `method`.
  */
-function defaultHandler(text, method) {
+function itDefaultHandler(text, method) {
+    try {
+        return method.apply(this);
+    } catch (err) {
+        if (err instanceof assert.AssertionError) {
+            err.message += ` (${util.inspect(err.actual)} ${err.operator} ${util.inspect(err.expected)})`;
+        }
+        throw err;
+    }
+}
+
+/**
+ * This is `describe` default handler if `describe` don't exist.
+ * @this {Mocha}
+ * @param {string} text - The description of the test case.
+ * @param {Function} method - The logic of the test case.
+ * @returns {any} Returned value of `method`.
+ */
+function describeDefaultHandler(text, method) {
     return method.apply(this);
 }
 
@@ -212,7 +230,7 @@ class RuleTester {
     static get describe() {
         return (
             this[DESCRIBE] ||
-            (typeof describe === "function" ? describe : defaultHandler)
+            (typeof describe === "function" ? describe : describeDefaultHandler)
         );
     }
 
@@ -223,7 +241,7 @@ class RuleTester {
     static get it() {
         return (
             this[IT] ||
-            (typeof it === "function" ? it : defaultHandler)
+            (typeof it === "function" ? it : itDefaultHandler)
         );
     }
 

tests/lib/testers/no-test-runners.js

@@ -0,0 +1,35 @@
+/**
+ * @fileoverview Tests for RuleTester without any test runner
+ * @author Weijia Wang <starkwang@126.com>
+ */
+"use strict";
+
+/* global describe, it */
+/* eslint-disable no-global-assign*/
+const assert = require("assert"),
+    RuleTester = require("../../../lib/testers/rule-tester");
+const tmpIt = it;
+const tmpDescribe = describe;
+
+it = null;
+describe = null;
+
+try {
+    const ruleTester = new RuleTester();
+
+    assert.throws(() => {
+        ruleTester.run("no-var", require("../../fixtures/testers/rule-tester/no-var"), {
+            valid: [
+                "bar = baz;"
+            ],
+            invalid: [
+                { code: "var foo = bar;", output: "invalid output", errors: 1 }
+            ]
+        });
+    }, /Output is incorrect\. \(' foo = bar;' == 'invalid output'\)$/);
+} catch (e) {
+    throw e;
+} finally {
+    it = tmpIt;
+    describe = tmpDescribe;
+}