Update: More detailed assert message for rule-tester

lib/testers/rule-tester.js

@@ -138,7 +138,14 @@ const IT = Symbol("it");
  * @returns {any} Returned value of `method`.
  */
 function defaultHandler(text, method) {
-    return method.apply(this);
+    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;
+    }
 }
 
 class RuleTester {

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

@@ -0,0 +1,31 @@
+/**
+ * @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;
+
+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 }
+        ]
+    });
+}, /' foo = bar;' == 'invalid output'/);
+
+it = tmpIt;
+describe = tmpDescribe;