Tests: purge settings cache

Some tests need to change settings, but since MemoryCacheSettingsRepository caches settings in-memory, those changes aren't reflected. The new `purgeSettingsCache` removes it from the container, eliminating that cache.

For UserTest, we also need to regenerate the display name driver, since that's set statically on boot, before we'll get a change to clear the settings cache.

php-packages/testing/tests/integration/UsesSettings.php

@@ -0,0 +1,25 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Tests\integration;
+
+use Flarum\Settings\SettingsRepositoryInterface;
+
+trait UsesSettings
+{
+    /**
+     * Removes the settings respository instance from the IoC container.
+     *
+     * This allows test cases that add/modify settings to refresh the in-memory settings cache.
+     */
+    protected function purgeSettingsCache()
+    {
+        $this->app()->getContainer()->forgetInstance(SettingsRepositoryInterface::class);
+    }
+}