I'm in a bit of a pickle
I want to create a webhook listener to Stripe's customer.subscription.trial_will_end event to send a customer an email letting them know billing will start and giving them cancellation info, but I can't work out how to test it works without waiting a day between each test, i.e. setting the trial period for 4 days, and the event being fired when there's 3 days left.
The Stripe docs give a method for testing trials, but this doesn't fit my use case as the only thing that doesn't work using that method is the trial_will_end event. The CLI can send webhook events, but again the trial_will_end event is not implemented.
How can I test this functionality without having to wait a full day between tests?
There are not currently great ways to manage time-dependent events like this. You will need to seed some test data to generate such events. For a given day of testing through, you can re-use a recent trial_will_end event (say evt_123) using the CLI resend function (doc):
stripe events resend evt_123 --webhook-endpoint we_321
This will let you re-test your endpoint to handle the event & send the email multiple times, ingesting the same event.