d6b3790d1a tests: check readability of cookie file (Chun Kuan Lee)
Pull request description:
This PR would wait until the `.cookie` file is readable
Possible fix no. 5 `PermissionError` in #14446
Tree-SHA512: e7055c7ca26a6eadbbe19e4eef08ffee61cd17de79b30af2f0d090f0ad81ca24815e3c7e034e5e30d47c580bb0b221b3955e9ff2fcec2274fbf7b9232ab0cdc7