[12.x] Introduce WithCachedRoutes testing trait

src/Illuminate/Foundation/Application.php

@@ -1322,7 +1322,8 @@ public function getCachedConfigPath()
      */
     public function routesAreCached()
     {
-        return $this['files']->exists($this->getCachedRoutesPath());
+        return ($this->bound('routes.cached') && $this->make('routes.cached') === true) ||
+            $this['files']->exists($this->getCachedRoutesPath());
     }
 
     /**

src/Illuminate/Foundation/Testing/CachedState.php

@@ -0,0 +1,8 @@
+<?php
+
+namespace Illuminate\Foundation\Testing;
+
+class CachedState
+{
+    public static array $cachedRoutes;
+}

src/Illuminate/Foundation/Testing/TestCase.php

@@ -29,6 +29,11 @@ public function createApplication()
     {
         $app = require Application::inferBasePath().'/bootstrap/app.php';
 
+        if (isset(CachedState::$cachedRoutes) &&
+            in_array(WithCachedRoutes::class, class_uses_recursive(static::class))) {
+            $app->booting(fn () => $this->markRoutesCached($app));
+        }
+
         $app->make(Kernel::class)->bootstrap();
 
         return $app;

src/Illuminate/Foundation/Testing/WithCachedRoutes.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace Illuminate\Foundation\Testing;
+
+use Illuminate\Foundation\Application;
+use Illuminate\Foundation\Support\Providers\RouteServiceProvider;
+
+trait WithCachedRoutes
+{
+    /**
+     * After creating the routes once, we can cache them for the remaining tests.
+     *
+     * @return void
+     */
+    protected function setUpWithCachedRoutes(): void
+    {
+        if ((CachedState::$cachedRoutes ?? null) === null) {
+            $routes = $this->app['router']->getRoutes();
+
+            $routes->refreshNameLookups();
+            $routes->refreshActionLookups();
+
+            CachedState::$cachedRoutes = $routes->compile();
+        }
+
+        $this->markRoutesCached($this->app);
+    }
+
+    /**
+     * Reset the route service provider so it's not defaulting to loading cached routes.
+     *
+     * This is helpful if some of the tests in the suite apply this trait while others do not.
+     *
+     * @return void
+     */
+    protected function tearDownWithCachedRoutes(): void
+    {
+        RouteServiceProvider::loadCachedRoutesUsing(null);
+    }
+
+    /**
+     * Inform the container to treat routes as cached.
+     */
+    protected function markRoutesCached(Application $app): void
+    {
+        $app->instance('routes.cached', true);
+
+        RouteServiceProvider::loadCachedRoutesUsing(
+            static fn () => app('router')->setCompiledRoutes(CachedState::$cachedRoutes)
+        );
+    }
+
+}

tests/Foundation/FoundationApplicationTest.php

@@ -609,6 +609,31 @@ public function testAbortAcceptsHeaders()
             $this->assertSame(['X-FOO' => 'BAR'], $exception->getHeaders());
         }
     }
+
+    public function test_routes_are_cached()
+    {
+        $app = new Application();
+        $app->instance('routes.cached', true);
+        $this->assertTrue($app->routesAreCached());
+    }
+
+    public function test_routes_are_not_cached_by_instance_falls_back_to_file()
+    {
+        $app = new Application();
+        $files = new class
+        {
+            public string $pathRequested;
+            public function exists(string $path): bool
+            {
+                $this->pathRequested = $path;
+                return false;
+            }
+        };
+        $app->instance('files', $files);
+
+        $this->assertFalse($app->routesAreCached());
+        $this->assertStringContainsString('routes-v7.php', $files->pathRequested);
+    }
 }
 
 class ApplicationBasicServiceProviderStub extends ServiceProvider