Stripe test clocks are the only supported way to simulate subscription renewals and trial ends

Subscription billing in test mode still follows real wall-clock time, so a monthly subscription created today does not renew for a month and a seven-day trial does not end for a week. Test clocks solve this: create a clock through the test helpers endpoint, attach a customer to it at customer creation with the test_clock field, then advance the clock to a future timestamp. Stripe replays the intervening billing cycle and emits the real events, including invoice.created, invoice.paid, customer.subscription.trial_will_end and customer.subscription.updated.

Advancing is asynchronous, so poll the clock until its status is ready before asserting. Clocks cannot move backward and a customer cannot be attached after it was created. Use them in integration tests instead of hand-written event fixtures, which drift from the real payload shapes.