The docblock in tests\bootstrap.php appears to have been copied from https://github.com/blobaugh/wordpress-plugin-tests
which uses a method of loading the plugin that's now been deprecated.

 * Edit 'active_plugins' setting below to point to your main plugin file.
 *
 * @package wordpress-plugin-tests

I would argue that both the instruction and package are wrong.

Also that the double slash comments that follow could be improved.

// Support for:
// 1. `WP_DEVELOP_DIR` environment variable
// 2. Plugin installed inside of WordPress.org developer checkout
// 3. Tests checked out to /tmp

Perhaps it's just a case of updating 1. to reference the environment variables that are tested before you go digging around.