In reply to David Anderson.

Hi David,

No, it doesn’t work that way. The “Tested up to” field is here to indicate on which maximum version of WP the plugin has been tested and this information is used to display a message indicating that the plugin has not been tested on this version of WordPress in the plugin installation screen, but that’s all. This is not used to actively prevent the installation of the plugin.

Worth noting that the only actively and officially supported version of WordPress being the latest version released, there is currently nothing preventing the installation of a plugin that does not indicate that it has been tested with the current version.

Have a look on the plugin installation screen, and scroll through the plugins list: there is a message to show if the plugin was tested or not with the current version of WP (= "Untested with your version of WordPress" for example), but you can always install it if you want to.