Unit Tests: Test for WP_Query should confirm before before unlisting the post that the post is available in results

[Nikschavan]

Is your feature request related to a problem? Please describe.

https://github.com/brainstormforce/unlist-posts/blob/0bef1f800cc8b21ffac31f9b0cc5ce971a39cbc1/tests/test-wp-query.php#L36-L41

Here we should assert that the post is available if WP_Query is run.