# Use Simulations to simulate Billing objects

Learn how to simulate Billing objects through time.

Test your Billing integration and make sure it behaves as expected. By running a simulation, you can see how various Billing resources like subscriptions change over time. For example, you can see how your setup handles a payment failure for a quarterly renewal.

Simulations use test clocks to control time. In the API and Dashboard, there are references to both. A simulation uses a clock to advance time, and track how things change.

Simulations let you:

- Test complex simulations such as upgrading or changing plans mid-cycle.
- Ensure your integration processes Billing lifecycle webhooks correctly.
- Validate that your app handles trials correctly.
- Build and test multi-phase subscription schedules.

## How to use test clocks

[Simulate subscriptions](https://docs.stripe.com/billing/testing/test-clocks/simulate-subscriptions.md): Learn how to simulate subscriptions in a sandbox.

[API and advanced usage](https://docs.stripe.com/billing/testing/test-clocks/api-advanced-usage.md): Learn advanced strategies for using test clocks in the Dashboard and API.