Apache .htaccess <Directory not allowed here

<Directory> directive is not allowed in .htaccess and for meeting your requirements you don't even need this in .htaccess.

You can use this rule in site root (parent) .htaccess:

RewriteEngine On

RewriteCond %{QUERY_STRING} !(?:^|&)test=yes(?:&|$) [NC]
RewriteRule ^foo/(.*)$ bar/$1?test=yes [NC,QSA,L]