update docblock + tests

src/Routing/Router.php

@@ -971,6 +971,9 @@ public static function scope($path, $params = [], $callback = null)
      * For example a path of `admin` would result in `'prefix' => 'admin'` being
      * applied to all connected routes.
      *
+     * The prefix name will be inflected to the underscore version to create
+     * the routing path. If you want a custom path name, use the `path` option.
+     *
      * You can re-open a prefix as many times as necessary, as well as nest prefixes.
      * Nested prefixes will result in prefix values like `admin/api` which translates
      * to the `Controller\Admin\Api\` namespace.

tests/TestCase/Routing/RouterTest.php

@@ -3104,6 +3104,12 @@ public function testPrefixOptions()
             $this->assertEquals('/admin', $routes->path());
             $this->assertEquals(['prefix' => 'admin', 'param' => 'value'], $routes->params());
         });
+
+        Router::prefix('CustomPath', ['path' => '/custom-path'], function ($routes) {
+            $this->assertInstanceOf('Cake\Routing\RouteBuilder', $routes);
+            $this->assertEquals('/custom-path', $routes->path());
+            $this->assertEquals(['prefix' => 'CustomPath'], $routes->params());
+        });
     }
 
     /**