diff --git a/src/ConfigureRoutes.php b/src/ConfigureRoutes.php
index bcd97fc..740a59b 100644
--- a/src/ConfigureRoutes.php
+++ b/src/ConfigureRoutes.php
@@ -23,14 +23,14 @@ interface ConfigureRoutes
      * @param string|string[] $httpMethod
      * @param ExtraParameters $extraParameters
      */
-    public function addRoute(string|array $httpMethod, string $route, mixed $handler, array $extraParameters = []): void;
+    public function addRoute(string|array $httpMethod, string $route, mixed $handler, array $extraParameters = []): static;
 
     /**
      * Create a route group with a common prefix.
      *
      * All routes created by the passed callback will have the given group prefix prepended.
      */
-    public function addGroup(string $prefix, callable $callback): void;
+    public function addGroup(string $prefix, callable $callback): static;
 
     /**
      * Adds a fallback route to the collection
@@ -39,7 +39,7 @@ public function addGroup(string $prefix, callable $callback): void;
      *
      * @param ExtraParameters $extraParameters
      */
-    public function any(string $route, mixed $handler, array $extraParameters = []): void;
+    public function any(string $route, mixed $handler, array $extraParameters = []): static;
 
     /**
      * Adds a GET route to the collection
@@ -48,7 +48,7 @@ public function any(string $route, mixed $handler, array $extraParameters = []):
      *
      * @param ExtraParameters $extraParameters
      */
-    public function get(string $route, mixed $handler, array $extraParameters = []): void;
+    public function get(string $route, mixed $handler, array $extraParameters = []): static;
 
     /**
      * Adds a POST route to the collection
@@ -57,7 +57,7 @@ public function get(string $route, mixed $handler, array $extraParameters = []):
      *
      * @param ExtraParameters $extraParameters
      */
-    public function post(string $route, mixed $handler, array $extraParameters = []): void;
+    public function post(string $route, mixed $handler, array $extraParameters = []): static;
 
     /**
      * Adds a PUT route to the collection
@@ -66,7 +66,7 @@ public function post(string $route, mixed $handler, array $extraParameters = [])
      *
      * @param ExtraParameters $extraParameters
      */
-    public function put(string $route, mixed $handler, array $extraParameters = []): void;
+    public function put(string $route, mixed $handler, array $extraParameters = []): static;
 
     /**
      * Adds a DELETE route to the collection
@@ -75,7 +75,7 @@ public function put(string $route, mixed $handler, array $extraParameters = []):
      *
      * @param ExtraParameters $extraParameters
      */
-    public function delete(string $route, mixed $handler, array $extraParameters = []): void;
+    public function delete(string $route, mixed $handler, array $extraParameters = []): static;
 
     /**
      * Adds a PATCH route to the collection
@@ -84,7 +84,7 @@ public function delete(string $route, mixed $handler, array $extraParameters = [
      *
      * @param ExtraParameters $extraParameters
      */
-    public function patch(string $route, mixed $handler, array $extraParameters = []): void;
+    public function patch(string $route, mixed $handler, array $extraParameters = []): static;
 
     /**
      * Adds a HEAD route to the collection
@@ -93,7 +93,7 @@ public function patch(string $route, mixed $handler, array $extraParameters = []
      *
      * @param ExtraParameters $extraParameters
      */
-    public function head(string $route, mixed $handler, array $extraParameters = []): void;
+    public function head(string $route, mixed $handler, array $extraParameters = []): static;
 
     /**
      * Adds an OPTIONS route to the collection
@@ -102,7 +102,7 @@ public function head(string $route, mixed $handler, array $extraParameters = [])
      *
      * @param ExtraParameters $extraParameters
      */
-    public function options(string $route, mixed $handler, array $extraParameters = []): void;
+    public function options(string $route, mixed $handler, array $extraParameters = []): static;
 
     /**
      * Returns the processed aggregated route data.
diff --git a/src/RouteCollector.php b/src/RouteCollector.php
index 9de94b6..845f1e9 100644
--- a/src/RouteCollector.php
+++ b/src/RouteCollector.php
@@ -4,31 +4,11 @@
 namespace FastRoute;
 
 use function array_key_exists;
-use function array_reverse;
-use function is_string;
 
-/**
- * @phpstan-import-type ProcessedData from ConfigureRoutes
- * @phpstan-import-type ExtraParameters from DataGenerator
- * @phpstan-import-type RoutesForUriGeneration from GenerateUri
- * @phpstan-import-type ParsedRoutes from RouteParser
- * @final
- */
-class RouteCollector implements ConfigureRoutes
+final class RouteCollector extends RouteCollectorAbstract
 {
-    protected string $currentGroupPrefix = '';
-
-    /** @var RoutesForUriGeneration */
-    private array $namedRoutes = [];
-
-    public function __construct(
-        protected readonly RouteParser $routeParser,
-        protected readonly DataGenerator $dataGenerator,
-    ) {
-    }
-
     /** @inheritDoc */
-    public function addRoute(string|array $httpMethod, string $route, mixed $handler, array $extraParameters = []): void
+    public function addRoute(string|array $httpMethod, string $route, mixed $handler, array $extraParameters = []): static
     {
         $route = $this->currentGroupPrefix . $route;
         $parsedRoutes = $this->routeParser->parse($route);
@@ -44,96 +24,18 @@ public function addRoute(string|array $httpMethod, string $route, mixed $handler
         if (array_key_exists(self::ROUTE_NAME, $extraParameters)) {
             $this->registerNamedRoute($extraParameters[self::ROUTE_NAME], $parsedRoutes);
         }
-    }
 
-    /** @param ParsedRoutes $parsedRoutes */
-    private function registerNamedRoute(mixed $name, array $parsedRoutes): void
-    {
-        if (! is_string($name) || $name === '') {
-            throw BadRouteException::invalidRouteName($name);
-        }
-
-        if (array_key_exists($name, $this->namedRoutes)) {
-            throw BadRouteException::namedRouteAlreadyDefined($name);
-        }
-
-        $this->namedRoutes[$name] = array_reverse($parsedRoutes);
+        return $this;
     }
 
-    public function addGroup(string $prefix, callable $callback): void
+    /** @inheritDoc */
+    public function addGroup(string $prefix, callable $callback): static
     {
         $previousGroupPrefix = $this->currentGroupPrefix;
         $this->currentGroupPrefix = $previousGroupPrefix . $prefix;
         $callback($this);
         $this->currentGroupPrefix = $previousGroupPrefix;
-    }
-
-    /** @inheritDoc */
-    public function any(string $route, mixed $handler, array $extraParameters = []): void
-    {
-        $this->addRoute('*', $route, $handler, $extraParameters);
-    }
-
-    /** @inheritDoc */
-    public function get(string $route, mixed $handler, array $extraParameters = []): void
-    {
-        $this->addRoute('GET', $route, $handler, $extraParameters);
-    }
-
-    /** @inheritDoc */
-    public function post(string $route, mixed $handler, array $extraParameters = []): void
-    {
-        $this->addRoute('POST', $route, $handler, $extraParameters);
-    }
-
-    /** @inheritDoc */
-    public function put(string $route, mixed $handler, array $extraParameters = []): void
-    {
-        $this->addRoute('PUT', $route, $handler, $extraParameters);
-    }
-
-    /** @inheritDoc */
-    public function delete(string $route, mixed $handler, array $extraParameters = []): void
-    {
-        $this->addRoute('DELETE', $route, $handler, $extraParameters);
-    }
 
-    /** @inheritDoc */
-    public function patch(string $route, mixed $handler, array $extraParameters = []): void
-    {
-        $this->addRoute('PATCH', $route, $handler, $extraParameters);
-    }
-
-    /** @inheritDoc */
-    public function head(string $route, mixed $handler, array $extraParameters = []): void
-    {
-        $this->addRoute('HEAD', $route, $handler, $extraParameters);
-    }
-
-    /** @inheritDoc */
-    public function options(string $route, mixed $handler, array $extraParameters = []): void
-    {
-        $this->addRoute('OPTIONS', $route, $handler, $extraParameters);
-    }
-
-    /** @inheritDoc */
-    public function processedRoutes(): array
-    {
-        $data =  $this->dataGenerator->getData();
-        $data[] = $this->namedRoutes;
-
-        return $data;
-    }
-
-    /**
-     * @deprecated
-     *
-     * @see ConfigureRoutes::processedRoutes()
-     *
-     * @return ProcessedData
-     */
-    public function getData(): array
-    {
-        return $this->processedRoutes();
+        return $this;
     }
 }
diff --git a/src/RouteCollectorAbstract.php b/src/RouteCollectorAbstract.php
new file mode 100644
index 0000000..66fc981
--- /dev/null
+++ b/src/RouteCollectorAbstract.php
@@ -0,0 +1,111 @@
+<?php
+declare(strict_types=1);
+
+namespace FastRoute;
+
+use function array_key_exists;
+use function array_reverse;
+use function is_string;
+
+/**
+ * @phpstan-import-type ProcessedData from ConfigureRoutes
+ * @phpstan-import-type ExtraParameters from DataGenerator
+ * @phpstan-import-type RoutesForUriGeneration from GenerateUri
+ * @phpstan-import-type ParsedRoutes from RouteParser
+ */
+abstract class RouteCollectorAbstract implements ConfigureRoutes
+{
+    protected string $currentGroupPrefix = '';
+
+    /** @var RoutesForUriGeneration */
+    protected array $namedRoutes = [];
+
+    public function __construct(
+        protected readonly RouteParser $routeParser,
+        protected DataGenerator $dataGenerator,
+    ) {
+    }
+
+    /** @param ParsedRoutes $parsedRoutes */
+    protected function registerNamedRoute(mixed $name, array $parsedRoutes): void
+    {
+        if (! is_string($name) || $name === '') {
+            throw BadRouteException::invalidRouteName($name);
+        }
+
+        if (array_key_exists($name, $this->namedRoutes)) {
+            throw BadRouteException::namedRouteAlreadyDefined($name);
+        }
+
+        $this->namedRoutes[$name] = array_reverse($parsedRoutes);
+    }
+
+    /** @inheritDoc */
+    public function processedRoutes(): array
+    {
+        $data =  $this->dataGenerator->getData();
+        $data[] = $this->namedRoutes;
+
+        return $data;
+    }
+
+    /**
+     * @deprecated
+     *
+     * @see ConfigureRoutes::processedRoutes()
+     *
+     * @return ProcessedData
+     */
+    public function getData(): array
+    {
+        return $this->processedRoutes();
+    }
+
+    /** @inheritDoc */
+    public function any(string $route, mixed $handler, array $extraParameters = []): static
+    {
+        return $this->addRoute('*', $route, $handler, $extraParameters);
+    }
+
+    /** @inheritDoc */
+    public function get(string $route, mixed $handler, array $extraParameters = []): static
+    {
+        return $this->addRoute('GET', $route, $handler, $extraParameters);
+    }
+
+    /** @inheritDoc */
+    public function post(string $route, mixed $handler, array $extraParameters = []): static
+    {
+        return $this->addRoute('POST', $route, $handler, $extraParameters);
+    }
+
+    /** @inheritDoc */
+    public function put(string $route, mixed $handler, array $extraParameters = []): static
+    {
+        return $this->addRoute('PUT', $route, $handler, $extraParameters);
+    }
+
+    /** @inheritDoc */
+    public function delete(string $route, mixed $handler, array $extraParameters = []): static
+    {
+        return $this->addRoute('DELETE', $route, $handler, $extraParameters);
+    }
+
+    /** @inheritDoc */
+    public function patch(string $route, mixed $handler, array $extraParameters = []): static
+    {
+        return $this->addRoute('PATCH', $route, $handler, $extraParameters);
+    }
+
+    /** @inheritDoc */
+    public function head(string $route, mixed $handler, array $extraParameters = []): static
+    {
+        return $this->addRoute('HEAD', $route, $handler, $extraParameters);
+    }
+
+    /** @inheritDoc */
+    public function options(string $route, mixed $handler, array $extraParameters = []): static
+    {
+        return $this->addRoute('OPTIONS', $route, $handler, $extraParameters);
+    }
+}
diff --git a/src/RouteCollectorImmutable.php b/src/RouteCollectorImmutable.php
new file mode 100644
index 0000000..55ff1f9
--- /dev/null
+++ b/src/RouteCollectorImmutable.php
@@ -0,0 +1,46 @@
+<?php
+declare(strict_types=1);
+
+namespace FastRoute;
+
+use function array_key_exists;
+
+final class RouteCollectorImmutable extends RouteCollectorAbstract
+{
+    /** @inheritDoc */
+    public function addRoute(string|array $httpMethod, string $route, mixed $handler, array $extraParameters = []): static
+    {
+        $clone = clone $this;
+        $clone->dataGenerator = clone $clone->dataGenerator;
+
+        $route = $clone->currentGroupPrefix . $route;
+        $parsedRoutes = $clone->routeParser->parse($route);
+
+        $extraParameters = [self::ROUTE_REGEX => $route] + $extraParameters;
+
+        foreach ((array) $httpMethod as $method) {
+            foreach ($parsedRoutes as $parsedRoute) {
+                $clone->dataGenerator->addRoute($method, $parsedRoute, $handler, $extraParameters);
+            }
+        }
+
+        if (array_key_exists(self::ROUTE_NAME, $extraParameters)) {
+            $clone->registerNamedRoute($extraParameters[self::ROUTE_NAME], $parsedRoutes);
+        }
+
+        return $clone;
+    }
+
+    /** @inheritDoc */
+    public function addGroup(string $prefix, callable $callback): static
+    {
+        $clone = clone $this;
+
+        $previousGroupPrefix = $clone->currentGroupPrefix;
+        $clone->currentGroupPrefix = $previousGroupPrefix . $prefix;
+        $clone = $callback($clone);
+        $clone->currentGroupPrefix = $previousGroupPrefix;
+
+        return $clone;
+    }
+}
diff --git a/test/RouteCollectorImmutableTest.php b/test/RouteCollectorImmutableTest.php
new file mode 100644
index 0000000..f45efcf
--- /dev/null
+++ b/test/RouteCollectorImmutableTest.php
@@ -0,0 +1,190 @@
+<?php
+declare(strict_types=1);
+
+namespace FastRoute\Test;
+
+use FastRoute\BadRouteException;
+use FastRoute\ConfigureRoutes;
+use FastRoute\DataGenerator;
+use FastRoute\RouteCollectorImmutable;
+use FastRoute\RouteParser\Std;
+use PHPUnit\Framework\Attributes as PHPUnit;
+use PHPUnit\Framework\TestCase;
+
+use function count;
+use function is_string;
+
+final class RouteCollectorImmutableTest extends TestCase
+{
+    #[PHPUnit\Test]
+    public function shortcutsCanBeUsedToRegisterRoutes(): void
+    {
+        $r = self::routeCollector();
+
+        $immutable = $r
+            ->any('/any', 'any')
+            ->delete('/delete', 'delete')
+            ->get('/get', 'get')
+            ->head('/head', 'head')
+            ->patch('/patch', 'patch')
+            ->post('/post', 'post')
+            ->put('/put', 'put')
+            ->options('/options', 'options');
+
+        $expected = [
+            ['*', '/any', 'any', ['_route' => '/any']],
+            ['DELETE', '/delete', 'delete', ['_route' => '/delete']],
+            ['GET', '/get', 'get', ['_route' => '/get']],
+            ['HEAD', '/head', 'head', ['_route' => '/head']],
+            ['PATCH', '/patch', 'patch', ['_route' => '/patch']],
+            ['POST', '/post', 'post', ['_route' => '/post']],
+            ['PUT', '/put', 'put', ['_route' => '/put']],
+            ['OPTIONS', '/options', 'options', ['_route' => '/options']],
+        ];
+
+        self::assertSame($expected, $immutable->processedRoutes()[0]);
+    }
+
+    #[PHPUnit\Test]
+    public function routesCanBeGrouped(): void
+    {
+        $r = self::routeCollector();
+
+        $immutable = $r
+            ->delete('/delete', 'delete')
+            ->get('/get', 'get')
+            ->head('/head', 'head')
+            ->patch('/patch', 'patch')
+            ->post('/post', 'post')
+            ->put('/put', 'put')
+            ->options('/options', 'options');
+
+        $immutable = $immutable->addGroup('/group-one', static function (ConfigureRoutes $r1): ConfigureRoutes {
+            $immutable1 = $r1
+                ->delete('/delete', 'delete')
+                ->get('/get', 'get')
+                ->head('/head', 'head')
+                ->patch('/patch', 'patch')
+                ->post('/post', 'post')
+                ->put('/put', 'put')
+                ->options('/options', 'options');
+
+            return $immutable1->addGroup('/group-two', static function (ConfigureRoutes $r2): ConfigureRoutes {
+                return $r2
+                    ->delete('/delete', 'delete')
+                    ->get('/get', 'get')
+                    ->head('/head', 'head')
+                    ->patch('/patch', 'patch')
+                    ->post('/post', 'post')
+                    ->put('/put', 'put')
+                    ->options('/options', 'options');
+            });
+        });
+
+        $immutable = $immutable->addGroup('/admin', static function (ConfigureRoutes $r): ConfigureRoutes {
+            return $r->get('-some-info', 'admin-some-info');
+        });
+
+        $immutable = $immutable->addGroup('/admin-', static function (ConfigureRoutes $r): ConfigureRoutes {
+            return $r->get('more-info', 'admin-more-info');
+        });
+
+        $expected = [
+            ['DELETE', '/delete', 'delete', ['_route' => '/delete']],
+            ['GET', '/get', 'get', ['_route' => '/get']],
+            ['HEAD', '/head', 'head', ['_route' => '/head']],
+            ['PATCH', '/patch', 'patch', ['_route' => '/patch']],
+            ['POST', '/post', 'post', ['_route' => '/post']],
+            ['PUT', '/put', 'put', ['_route' => '/put']],
+            ['OPTIONS', '/options', 'options', ['_route' => '/options']],
+            ['DELETE', '/group-one/delete', 'delete', ['_route' => '/group-one/delete']],
+            ['GET', '/group-one/get', 'get', ['_route' => '/group-one/get']],
+            ['HEAD', '/group-one/head', 'head', ['_route' => '/group-one/head']],
+            ['PATCH', '/group-one/patch', 'patch', ['_route' => '/group-one/patch']],
+            ['POST', '/group-one/post', 'post', ['_route' => '/group-one/post']],
+            ['PUT', '/group-one/put', 'put', ['_route' => '/group-one/put']],
+            ['OPTIONS', '/group-one/options', 'options', ['_route' => '/group-one/options']],
+            ['DELETE', '/group-one/group-two/delete', 'delete', ['_route' => '/group-one/group-two/delete']],
+            ['GET', '/group-one/group-two/get', 'get', ['_route' => '/group-one/group-two/get']],
+            ['HEAD', '/group-one/group-two/head', 'head', ['_route' => '/group-one/group-two/head']],
+            ['PATCH', '/group-one/group-two/patch', 'patch', ['_route' => '/group-one/group-two/patch']],
+            ['POST', '/group-one/group-two/post', 'post', ['_route' => '/group-one/group-two/post']],
+            ['PUT', '/group-one/group-two/put', 'put', ['_route' => '/group-one/group-two/put']],
+            ['OPTIONS', '/group-one/group-two/options', 'options', ['_route' => '/group-one/group-two/options']],
+            ['GET', '/admin-some-info', 'admin-some-info', ['_route' => '/admin-some-info']],
+            ['GET', '/admin-more-info', 'admin-more-info', ['_route' => '/admin-more-info']],
+        ];
+
+        self::assertSame($expected, $immutable->processedRoutes()[0]);
+    }
+
+    #[PHPUnit\Test]
+    public function namedRoutesShouldBeRegistered(): void
+    {
+        $r = self::routeCollector();
+
+        $immutable = $r->get('/', 'index-handler', ['_name' => 'index']);
+        $immutable = $immutable->get('/users/me', 'fetch-user-handler', ['_name' => 'users.fetch']);
+
+        self::assertSame(['index' => [['/']], 'users.fetch' => [['/users/me']]], $immutable->processedRoutes()[2]);
+    }
+
+    #[PHPUnit\Test]
+    public function cannotDefineRouteWithEmptyName(): void
+    {
+        $r = self::routeCollector();
+
+        $this->expectException(BadRouteException::class);
+
+        $r->get('/', 'index-handler', ['_name' => '']);
+    }
+
+    #[PHPUnit\Test]
+    public function cannotDefineRouteWithInvalidTypeAsName(): void
+    {
+        $r = self::routeCollector();
+
+        $this->expectException(BadRouteException::class);
+
+        $r->get('/', 'index-handler', ['_name' => false]);
+    }
+
+    #[PHPUnit\Test]
+    public function cannotDefineDuplicatedRouteName(): void
+    {
+        $r = self::routeCollector();
+
+        $this->expectException(BadRouteException::class);
+
+        $immutable = $r->get('/', 'index-handler', ['_name' => 'index']);
+        $immutable->get('/users/me', 'fetch-user-handler', ['_name' => 'index']);
+    }
+
+    private static function routeCollector(): ConfigureRoutes
+    {
+        return new RouteCollectorImmutable(new Std(), self::dummyDataGenerator());
+    }
+
+    private static function dummyDataGenerator(): DataGenerator
+    {
+        return new class implements DataGenerator
+        {
+            /** @var list<array{string, string, mixed, array<string, bool|float|int|string>}> */
+            private array $routes = [];
+
+            /** @inheritDoc */
+            public function getData(): array
+            {
+                return [$this->routes, []];
+            }
+
+            /** @inheritDoc */
+            public function addRoute(string $httpMethod, array $routeData, mixed $handler, array $extraParameters = []): void
+            {
+                TestCase::assertTrue(count($routeData) === 1 && is_string($routeData[0]));
+
+                $this->routes[] = [$httpMethod, $routeData[0], $handler, $extraParameters];
+            }
+        };
+    }
+}
diff --git a/test/RouteCollectorTest.php b/test/RouteCollectorTest.php
index 4dd52ce..0e4f411 100644
--- a/test/RouteCollectorTest.php
+++ b/test/RouteCollectorTest.php
@@ -11,7 +11,6 @@
 use PHPUnit\Framework\Attributes as PHPUnit;
 use PHPUnit\Framework\TestCase;
 
-use function assert;
 use function count;
 use function is_string;
 
@@ -20,17 +19,17 @@ final class RouteCollectorTest extends TestCase
     #[PHPUnit\Test]
     public function shortcutsCanBeUsedToRegisterRoutes(): void
     {
-        $dataGenerator = self::dummyDataGenerator();
-        $r = new RouteCollector(new Std(), $dataGenerator);
-
-        $r->any('/any', 'any');
-        $r->delete('/delete', 'delete');
-        $r->get('/get', 'get');
-        $r->head('/head', 'head');
-        $r->patch('/patch', 'patch');
-        $r->post('/post', 'post');
-        $r->put('/put', 'put');
-        $r->options('/options', 'options');
+        $r = self::routeCollector();
+
+        $r
+            ->any('/any', 'any')
+            ->delete('/delete', 'delete')
+            ->get('/get', 'get')
+            ->head('/head', 'head')
+            ->patch('/patch', 'patch')
+            ->post('/post', 'post')
+            ->put('/put', 'put')
+            ->options('/options', 'options');
 
         $expected = [
             ['*', '/any', 'any', ['_route' => '/any']],
@@ -43,47 +42,49 @@ public function shortcutsCanBeUsedToRegisterRoutes(): void
             ['OPTIONS', '/options', 'options', ['_route' => '/options']],
         ];
 
-        self::assertObjectHasProperty('routes', $dataGenerator);
-        self::assertSame($expected, $dataGenerator->routes);
+        self::assertSame($expected, $r->processedRoutes()[0]);
     }
 
     #[PHPUnit\Test]
     public function routesCanBeGrouped(): void
     {
-        $dataGenerator = self::dummyDataGenerator();
-        $r = new RouteCollector(new Std(), $dataGenerator);
-
-        $r->delete('/delete', 'delete');
-        $r->get('/get', 'get');
-        $r->head('/head', 'head');
-        $r->patch('/patch', 'patch');
-        $r->post('/post', 'post');
-        $r->put('/put', 'put');
-        $r->options('/options', 'options');
-
-        $r->addGroup('/group-one', static function (ConfigureRoutes $r): void {
-            $r->delete('/delete', 'delete');
-            $r->get('/get', 'get');
-            $r->head('/head', 'head');
-            $r->patch('/patch', 'patch');
-            $r->post('/post', 'post');
-            $r->put('/put', 'put');
-            $r->options('/options', 'options');
-
-            $r->addGroup('/group-two', static function (ConfigureRoutes $r): void {
-                $r->delete('/delete', 'delete');
-                $r->get('/get', 'get');
-                $r->head('/head', 'head');
-                $r->patch('/patch', 'patch');
-                $r->post('/post', 'post');
-                $r->put('/put', 'put');
-                $r->options('/options', 'options');
+        $r = self::routeCollector();
+
+        $r
+            ->delete('/delete', 'delete')
+            ->get('/get', 'get')
+            ->head('/head', 'head')
+            ->patch('/patch', 'patch')
+            ->post('/post', 'post')
+            ->put('/put', 'put')
+            ->options('/options', 'options');
+
+        $r->addGroup('/group-one', static function (ConfigureRoutes $r1): void {
+            $r1
+                ->delete('/delete', 'delete')
+                ->get('/get', 'get')
+                ->head('/head', 'head')
+                ->patch('/patch', 'patch')
+                ->post('/post', 'post')
+                ->put('/put', 'put')
+                ->options('/options', 'options');
+
+            $r1->addGroup('/group-two', static function (ConfigureRoutes $r2): void {
+                $r2
+                    ->delete('/delete', 'delete')
+                    ->get('/get', 'get')
+                    ->head('/head', 'head')
+                    ->patch('/patch', 'patch')
+                    ->post('/post', 'post')
+                    ->put('/put', 'put')
+                    ->options('/options', 'options');
             });
         });
 
         $r->addGroup('/admin', static function (ConfigureRoutes $r): void {
             $r->get('-some-info', 'admin-some-info');
         });
+
         $r->addGroup('/admin-', static function (ConfigureRoutes $r): void {
             $r->get('more-info', 'admin-more-info');
         });
@@ -114,16 +115,14 @@ public function routesCanBeGrouped(): void
             ['GET', '/admin-more-info', 'admin-more-info', ['_route' => '/admin-more-info']],
         ];
 
-        self::assertObjectHasProperty('routes', $dataGenerator);
-        self::assertSame($expected, $dataGenerator->routes);
+        self::assertSame($expected, $r->processedRoutes()[0]);
     }
 
     #[PHPUnit\Test]
     public function namedRoutesShouldBeRegistered(): void
     {
-        $dataGenerator = self::dummyDataGenerator();
+        $r = self::routeCollector();
 
-        $r = new RouteCollector(new Std(), $dataGenerator);
         $r->get('/', 'index-handler', ['_name' => 'index']);
         $r->get('/users/me', 'fetch-user-handler', ['_name' => 'users.fetch']);
 
@@ -133,48 +132,56 @@ public function namedRoutesShouldBeRegistered(): void
     #[PHPUnit\Test]
     public function cannotDefineRouteWithEmptyName(): void
     {
-        $r = new RouteCollector(new Std(), self::dummyDataGenerator());
+        $r = self::routeCollector();
 
         $this->expectException(BadRouteException::class);
+
         $r->get('/', 'index-handler', ['_name' => '']);
     }
 
     #[PHPUnit\Test]
     public function cannotDefineRouteWithInvalidTypeAsName(): void
     {
-        $r = new RouteCollector(new Std(), self::dummyDataGenerator());
+        $r = self::routeCollector();
 
         $this->expectException(BadRouteException::class);
+
         $r->get('/', 'index-handler', ['_name' => false]);
     }
 
     #[PHPUnit\Test]
     public function cannotDefineDuplicatedRouteName(): void
     {
-        $r = new RouteCollector(new Std(), self::dummyDataGenerator());
+        $r = self::routeCollector();
 
         $this->expectException(BadRouteException::class);
+
         $r->get('/', 'index-handler', ['_name' => 'index']);
         $r->get('/users/me', 'fetch-user-handler', ['_name' => 'index']);
     }
 
+    private static function routeCollector(): ConfigureRoutes
+    {
+        return new RouteCollector(new Std(), self::dummyDataGenerator());
+    }
+
     private static function dummyDataGenerator(): DataGenerator
     {
         return new class implements DataGenerator
         {
             /** @var list<array{string, string, mixed, array<string, bool|float|int|string>}> */
-            public array $routes = [];
+            private array $routes = [];
 
             /** @inheritDoc */
             public function getData(): array
             {
-                return [[], []];
+                return [$this->routes, []];
             }
 
             /** @inheritDoc */
             public function addRoute(string $httpMethod, array $routeData, mixed $handler, array $extraParameters = []): void
             {
-                assert(count($routeData) === 1 && is_string($routeData[0]));
+                TestCase::assertTrue(count($routeData) === 1 && is_string($routeData[0]));
 
                 $this->routes[] = [$httpMethod, $routeData[0], $handler, $extraParameters];
             }