public function testCompareVersions()
 {
     // Necessary to avoid
     $oldCleanerClass = Diff::$html_cleaner_class;
     Diff::$html_cleaner_class = 'SiteTreeTest_NullHtmlCleaner';
     $page = new Page();
     $page->write();
     $this->assertEquals(1, $page->Version);
     // Use inline element to avoid double wrapping applied to
     // blocklevel elements depending on HTMLCleaner implementation:
     // <ins><p> gets converted to <ins><p><inst>
     $page->Content = "<span>This is a test</span>";
     $page->write();
     $this->assertEquals(2, $page->Version);
     $diff = $page->compareVersions(1, 2);
     $processedContent = trim($diff->Content);
     $processedContent = preg_replace('/\\s*</', '<', $processedContent);
     $processedContent = preg_replace('/>\\s*/', '>', $processedContent);
     $this->assertEquals("<ins><span>This is a test</span></ins>", $processedContent);
     Diff::$html_cleaner_class = $oldCleanerClass;
 }