hook_theme_suggestions_hook_alter() not working for Views
Found the solution. As it turns out, for some reason Drupal doesn't play nicely with custom theme suggestions starting with a word + single dash.

I updated my HOOK_theme_suggestions_HOOK_alter() function to include $suggestions[] = 'test__template'; (with 2 underscores between the words) and updated my template name to test--template.html.twig (with 2 dashes to match the 2 underscores), and everything works as expected.