Command line option --check can be used to perform a task or run a playbook in dry run mode, meaning that no changes will be made on the manage nodes (e.g. target systems). For example, here is how to use the --check option with the ansible-playbook command.

ansible-playbook foo.yml --check

Or, the check_mode module can be used to determine if a task would have been successful. In this example, check mode is used to determine if foo.txt can be copied.

- name: copy foo.txt
  copy:
    src: /tmp/foo.txt
    dest: /tmp/foo.txt
    owner: foo
    group: foo
    mode: '0644'
  check_mode: yes