Reset test state for modified config options

_config/tests.yml

@@ -9,6 +9,7 @@ SilverStripe\Core\Injector\Injector:
         extensions: '%$SilverStripe\Dev\State\ExtensionTestState'
         flushable: '%$SilverStripe\Dev\State\FlushableTestState'
         requirements: '%$SilverStripe\View\Dev\RequirementsTestState'
+        ssviewer: '%$SilverStripe\View\Dev\SSViewerTestState'
 ---
 Name: kerneltest
 Before: '*'

src/Control/ContentNegotiator.php

@@ -39,35 +39,29 @@ class ContentNegotiator
 
     /**
      * @config
-     *
      * @var string
      */
     private static $content_type = '';
 
     /**
      * @config
-     *
      * @var string
      */
     private static $encoding = 'utf-8';
 
     /**
      * @config
-     *
      * @var bool
      */
     private static $enabled = false;
 
     /**
-     * @config
-     *
      * @var bool
      */
     protected static $current_enabled = null;
 
     /**
      * @config
-     *
      * @var string
      */
     private static $default_format = 'html';

src/View/Dev/SSViewerTestState.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace SilverStripe\View\Dev;
+
+use SilverStripe\Control\ContentNegotiator;
+use SilverStripe\Dev\SapphireTest;
+use SilverStripe\Dev\State\TestState;
+use SilverStripe\View\SSViewer;
+
+class SSViewerTestState implements TestState
+{
+    public function setUp(SapphireTest $test)
+    {
+        SSViewer::set_themes(null);
+        SSViewer::setRewriteHashLinksDefault(null);
+        ContentNegotiator::setEnabled(null);
+    }
+
+    public function tearDown(SapphireTest $test)
+    {
+    }
+
+    public function setUpOnce($class)
+    {
+    }
+
+    public function tearDownOnce($class)
+    {
+    }
+}