Wordpress - How to test wp_cron?

My favorite plugin for that is Core Control which has very nice module for display of what is going in the cron - which events are set up, when are they next firing, etc.

On getting your hands dirty level see _get_cron_array(), which returns internal stored data for cron events (top level of keys are timestamps).

wp-cli is another way:

Listing Events

> wp cron event list
+-------------------+---------------------+-----------------------+---------------+
| hook              | next_run_gmt        | next_run_relative     | recurrence    |
+-------------------+---------------------+-----------------------+---------------+
| wp_update_plugins | 2020-04-14 08:11:38 | 7 hours 24 minutes    | 12 hours      |
| wp_update_themes  | 2020-04-14 08:11:38 | 7 hours 24 minutes    | 12 hours      |
| wcsc_prime_sites  | 2020-04-14 17:00:55 | 16 hours 13 minutes   | 1 day         |
+-------------------+---------------------+-----------------------+---------------+

Schedule an Event

> wp cron event schedule wp_update_plugins "now +5 seconds"
Success: Scheduled event with hook 'wp_update_plugins' for 2020-04-14 00:43:54 GMT.

Then you can visit the front-end of the site and refresh a couple times to make sure it's triggered. Then run list again to see that it's no longer scheduled.

Run Directly in Terminal

> wp cron event run wcsc_prime_sites
Executed the cron event 'wcsc_prime_sites' in 0.805s.
Success: Executed a total of 1 cron event.

One quirk to be aware of is that wp-cli runs in the wp-admin context, but WP Cron runs on the front end. That usually isn't a problem, but when you're writing jobs, make sure that you require() any wp-admin/includes files that your code expects to be loaded.

If you don't, then the job will work fine in wp-cli, but will produce a fatal error when running normally.

Other commands

Run wp help cron for more details.