Let's say you have a task that should only be executed when /tmp/foo is or is not a directory. The stat module and the register parameter can be used to store the statistics of /tmp/foo in a variable.

---
- hosts: all
  tasks:
    - name: "store the statistics of /opt/example.txt in the 'out' variable"
      stat:
        path: "/tmp/foo.txt"
      register: out

The debug module can be used to displays the out variable.

- name: display the 'out' variable
  debug: 
    var: out

Which should return something like this. Notice in this example the "isdir" is true.

TASK [debug] 
ok: [server1.example.com] => {
    "out": {
        "changed": false,
        "failed": false,
        "stat": {
            "atime": 1610186400.7513745,
            "attr_flags": "",
            "attributes": [],
            "block_size": 4096,
            "blocks": 8,
            "charset": "binary",
            "ctime": 1610187202.1764085,
            "dev": 64768,
            "device_type": 0,
            "executable": true,
            "exists": true,
            "gid": 0,
            "gr_name": "root",
            "inode": 50331777,
            "isblk": false,
            "ischr": false,
            "isdir": true,
            "isfifo": false,
            "isgid": false,
            "islnk": false,
            "isreg": false,
            "issock": false,
            "isuid": false,
            "mimetype": "inode/directory",
            "mode": "1777",
            "mtime": 1610187202.1764085,
            "nlink": 10,
            "path": "/tmp/foo",
            "pw_name": "root",
            "readable": true,
            "rgrp": true,
            "roth": true,
            "rusr": true,
            "size": 4096,
            "uid": 0,
            "version": "1309840072",
            "wgrp": true,
            "woth": true,
            "writeable": true,
            "wusr": true,
            "xgrp": true,
            "xoth": true,
            "xusr": true
        }
    }
}

The fail module and when parameter with out.stat.isdir can now be used to fail if /tmp/foo is or is not a directory.

- name: fail when /tmp/foo is a directory
  fail: 
   msg: /tmp/foo is a directory
  when: out.stat.isdir == true

Invoking this playbook should return something like this. The ansible-doc fail command can be used to show the Ansible documention on the fail module.

When fail evaluates to true, all of the subsequent tasks are skipped.

PLAY [all]

TASK [store the statistics of /tmp/foo in the 'out' variable]
ok: [server1.example.com]

TASK [fail when /tmp/foo is a directory]
fatal: [server1.example.com]: FAILED => {"changed": false, "msg": "/tmp/foo is a directory"}

PLAY RECAP
server1.example.com : ok=2  changed=0  unreacable=0  failed=1