Notice: wp_enqueue_style was called incorrectly

Stylesheet in WordPress plugin:

$plugin_dir = "test";
wp_enqueue_style('style', plugins_url("/" . $plugin_dir . "/css/style.css"), array(), null, null);

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When this is ran I get a notice warning:

Notice: wp_enqueue_style was called incorrectly. Scripts and styles should not be registered or enqueued until the wp_enqueue_scripts, admin_enqueue_scripts, or login_enqueue_scripts hooks. Please see Debugging in WordPress for more information. (This message was added in version 3.3.0.) in /home/username/public_html/wp/wp-includes/functions.php on line 4147

I have spent several hours on google trying different combos but it keeps falling back to this warning.

Note: I am looking for a solution in the plugin folder only. I do not want to mess with the theme. I have another same issue with a script and solving this will also solve another problem I have.