/**
  * @covers WPSEO_Frontend::flush_cache
  */
 public function test_flush_cache()
 {
     $c = self::$class_instance;
     // should not run when output buffering is not turned on
     $this->assertFalse(self::$class_instance->flush_cache());
     // turn on output buffering
     self::$class_instance->force_rewrite_output_buffer();
     $content = '<!DOCTYPE><html><head><title>TITLETOBEREPLACED</title>' . self::$class_instance->debug_marker(false) . '</head><body>Some body content. Should remain unchanged.</body></html>';
     // create expected output
     global $sep;
     $title = self::$class_instance->title('', $sep);
     $expected = preg_replace('/<title(.*)\\/title>/i', '', $content);
     $expected = str_replace($c->debug_marker(false), $c->debug_marker(false) . "\n" . '<title>' . $title . '</title>', $expected);
     echo $content;
     // run function
     $result = self::$class_instance->flush_cache();
     // run assertions
     $this->expectOutput($expected, $result);
     $this->assertTrue($result);
 }