I'm trying to show a message for specific content type through a new module, on Drupal 8.3.0. (I'm a beginner.) 

This is part of the code I am using.

### File test_module.module (updated code, still not working)

    /**
     * @file
     * Implementation of hook_node_view();
     */
    
    function test_module_node_view($node, $view_mode) {
      if ($view_mode == 'full' && $node->type == 'test_content') {
          /*Message with current date and time*/
          $current_time = time();
          drupal_set_message(t('Hello! Today is '.format_date($current_time,'medium')));
        }
      }

As far as I know, this should work, but it doesn't and I don't know why. The message is not showing for a node of content type "test_content". How can I fix this? Is there another way to alter nodes of custom content types?

> [![screenshot][1]][1]

<!-- break -->

> [![screenshot][2]][2]

(Test_content_example is a node of type 'test_content', so there should be a system message displayed, but there's none.)








  [1]: https://i.sstatic.net/QB9vg.png
  [2]: https://i.sstatic.net/ml7Tx.png