Why can only the root user access the existing files in a directory, despite existing ACLs?

Issue

Users can not access a directory content, even if they have a ACL with such permission.

Sample error:

    [testuser@server01 ~]$ ls /testdir
    ls: /testdir: Permission denied

getfacl returns:

    [testuser@server01 ~]$ getfacl /testdir
    getfacl: Removing leading '/' from absolute path names
    # file: testdir
    # owner: root
    # group: root
    user::rwx
    user:testuser:rwx           #effective:---
    group::r-x          #effective:---
    mask::---
    other::---