test: fix RuleTester test without test runners (#20631)

* test: fix `RuleTester` test without test runners

* account for different message in Node.js v20

Author: fasttime

tests/fixtures/testers/rule-tester/no-test-runners.js

@@ -0,0 +1,34 @@
+/**
+ * @fileoverview Tests for RuleTester without any test runner
+ * @author Weijia Wang <starkwang@126.com>
+ */
+"use strict";
+
+const assert = require("node:assert");
+const { RuleTester } = require("../../../../lib/rule-tester");
+
+const ruleTester = new RuleTester();
+
+assert.throws(
+	() => {
+		ruleTester.run("no-var", require("./no-var"), {
+			valid: ["bar = baz;"],
+			invalid: [
+				{
+					code: "var foo = bar;",
+					output: "invalid output",
+					errors: 1,
+				},
+			],
+		});
+	},
+	{
+		constructor: assert.AssertionError,
+		actual: " foo = bar;",
+		expected: "invalid output",
+		operator: "strictEqual",
+		message: process.version.startsWith("v20.")
+			? "Output is incorrect.\n+ actual - expected\n\n+ ' foo = bar;'\n- 'invalid output' (' foo = bar;' strictEqual 'invalid output')"
+			: "Output is incorrect.\n+ actual - expected\n\n+ ' foo = bar;'\n- 'invalid output'\n (' foo = bar;' strictEqual 'invalid output')",
+	},
+);

tests/lib/rule-tester/no-test-runners.js

@@ -4489,6 +4489,21 @@ describe("RuleTester", () => {
 		}, /A fatal parsing error occurred in autofix.\nError: .+\nAutofix output:\n.+/u);
 	});
 
+	it("should throw an error with expected message without a test runner", done => {
+		const { execFile } = require("node:child_process");
+
+		execFile(
+			process.execPath,
+			[
+				require.resolve(
+					"../../fixtures/testers/rule-tester/no-test-runners",
+				),
+			],
+			{ timeout: 1000 },
+			done,
+		);
+	});
+
 	describe("type checking", () => {
 		it('should throw if "only" property is not a boolean', () => {
 			// "only" has to be falsy as itOnly is not mocked for all test cases