Fix tests

src/Composer/Factory.php

@@ -289,7 +289,9 @@ class Factory
         $composer->setPluginManager($pm);
 
         // purge packages if they have been deleted on the filesystem
-        $this->purgePackages($rm->getLocalRepository(), $im);
+        if ($rm->getLocalRepository()) {
+            $this->purgePackages($rm->getLocalRepository(), $im);
+        }
 
         if (!$disablePlugins) {
             $pm->loadInstalledPlugins();

tests/Composer/Test/Mock/FactoryMock.php

@@ -16,6 +16,7 @@ use Composer\Config;
 use Composer\Factory;
 use Composer\Repository;
 use Composer\Repository\RepositoryManager;
+use Composer\Repository\WritableRepositoryInterface;
 use Composer\Installer;
 use Composer\IO\IOInterface;
 
@@ -46,7 +47,7 @@ class FactoryMock extends Factory
     {
     }
 
-    protected function purgePackages(Repository\RepositoryManager $rm, Installer\InstallationManager $im)
+    protected function purgePackages(WritableRepositoryInterface $repo, Installer\InstallationManager $im)
     {
     }
 }