Trigger renewal order emails for WooCommerce subscriptions for testing

To trigger an off-schedule renewal and therefore trigger the renewal order email, please follow these steps:

1. Purchase the test subscription with either Stripe or a gateway that requires manual renewal payments (e.g. Cheque, Bank transfer). PayPal won’t work.
2. Find the subscription key for the newly purchased subscription.
3. Delete the wcs_blocker_{$user_id}_($subscription_key} transient from the database (where $user_id is the ID of the customer who purchased the subscription).
4. Install & activate the WP-Crontrol plugin
5. Visit the Tools > Crontrol admin screen
6. Find the WP-Cron job with the scheduled_subscription_payment hook and matching user ID & subscription key to the test subscription.
7. Click the Run Now link next to the appropriate WP-Cron job

And that should trigger the renewal early.

This may sound harder than it should be to simply trigger a renewal order email, but there are safeguards to ensure payments are not charged on an incorrect schedule, so to force payments to charge out-of-schedule, you have to remove those safeguards and then trigger the renewal.