[5.4] Add ability to keep old files when testing uploads [second atte…

…mpt] (#19859)

* Add ability to keep old files when testing uploads

* Add persistentFake method

* Update Storage.php

src/Illuminate/Support/Facades/Storage.php

@@ -10,9 +10,10 @@
 class Storage extends Facade
 {
     /**
-     * Replace the given disk with a local, testing disk.
+     * Replace the given disk with a local testing disk.
      *
      * @param  string  $disk
+     *
      * @return void
      */
     public static function fake($disk)
@@ -24,6 +25,19 @@ public static function fake($disk)
         static::set($disk, self::createLocalDriver(['root' => $root]));
     }
 
+    /**
+     * Replace the given disk with a persistent local testing disk.
+     *
+     * @param  string  $disk
+     * @return void
+     */
+    public static function persistentFake($disk)
+    {
+        static::set($disk, self::createLocalDriver([
+            'root' => storage_path('framework/testing/disks/' . $disk)
+        ]));
+    }
+
     /**
      * Get the registered name of the component.
      *