add Less styles support to test coverage

tools/modern-tests/apps/react-router/imports/ui/App.jsx

@@ -5,6 +5,7 @@ import {
   Route,
   createRoutesFromElements,
 } from "react-router-dom";
+import "./Global.less";
 
 // Dynamically import components
 const Home = lazy(() =>

tools/modern-tests/apps/react-router/imports/ui/Global.less

@@ -0,0 +1,3 @@
+body {
+    white-space: break-spaces;
+}

tools/modern-tests/apps/react-router/package.json

@@ -17,12 +17,14 @@
     "react-router-dom": "^7.0.0"
   },
   "devDependencies": {
-    "playwright": "^1.54.2",
     "@babel/plugin-syntax-jsx": "^7.27.1",
     "@babel/preset-env": "^7.23.5",
     "@babel/preset-react": "^7.23.3",
     "babel-plugin-react-compiler": "^19.1.0-rc.2",
-    "babel-loader": "^9.1.3"
+    "babel-loader": "^9.1.3",
+    "less": "^4.4.0",
+    "less-loader": "^12.3.0",
+    "playwright": "^1.54.2"
   },
   "meteor": {
     "mainModule": {

tools/modern-tests/apps/react-router/rspack.config.js

@@ -25,6 +25,15 @@ export default defineConfig(Meteor => {
           ],
           type: 'javascript/auto',
         },
+        {
+          test: /\.less$/,
+          use: [
+            {
+              loader: 'less-loader',
+            },
+          ],
+          type: 'css/auto',
+        },
       ],
     },
   };

tools/modern-tests/react-router.test.js

@@ -9,7 +9,7 @@ import {
 import { testMeteorBundler, testMeteorRspackBundler } from './test-helpers';
 import fs from 'fs-extra';
 import path from 'path';
-import { assertMeteorReactApp } from "./assertions";
+import { assertBodyStyles, assertMeteorReactApp } from "./assertions";
 
 describe('ReactRouter App Bundling /', () => {
   describe('Meteor+Rspack Bundler /', testMeteorRspackBundler({
@@ -25,6 +25,10 @@ describe('ReactRouter App Bundling /', () => {
         await waitForReactEnvs(result.outputLines, { isJsxEnabled: true });
         await waitForMeteorOutput(result.outputLines, /.*babel-plugin-react-compiler.*/);
         await assert404Page(port);
+        // Less styles support
+        await assertBodyStyles({
+          'white-space': 'break-spaces',
+        });
       },
       afterRunRebuildClient: async ({ allConsoleLogs }) => {
         // Check for HMR output as enabled by default
@@ -34,6 +38,10 @@ describe('ReactRouter App Bundling /', () => {
         await waitForReactEnvs(result.outputLines, { isJsxEnabled: true });
         await waitForMeteorOutput(result.outputLines, /.*babel-plugin-react-compiler.*/);
         await assert404Page(port, { isProductionMode: true });
+        // Less styles support
+        await assertBodyStyles({
+          'white-space': 'break-spaces',
+        });
       },
       afterRunProductionRebuildClient: async ({ allConsoleLogs }) => {
         // Check for HMR to not be enabled in production-like mode