Side Effect

You might say

A user is only previewing a price. Do not silently write an order or send email; do that only after explicit submission.

A function or request changes external state or triggers an external action beyond returning a valueA price preview can calculate and return shipping without creating a quote or sending email. Saving the order and notifying the user are intentional side effects when the user explicitly submits. A side effect is not automatically an error; it needs a clear trigger and observable result.

How can a price preview avoid saving and notifying silently?

Quote preview and submitClick Preview

returned quote$1,280

databasedraft inserted

emailsent

EvidenceExternal state changed beyond the return value

A preview unexpectedly writes data and sends mail.

How the case moves from failure to a verifiable result

Problem and key mechanism: The user only wants a shipping and total preview, but the old endpoint writes a quote and sends email; separate preview calculation from explicit submission so Confirm order alone saves and notifies.

How to observe the improvement: Save the order, decrement stock, or send notifications only after explicit confirmation, and return the real status of each action. Verify that preview adds no record or email, while one confirmed submission creates the expected record and notification once.

A second scenario: content publishing: Previewing an article should not publish the draft or notify subscribers. Those external changes should wait for an explicit Publish action, with the publication state and notification result checked separately.

Quick checkChoose the best answer

The preview endpoint adds a quote and sends email on every call. What is the best adjustment?

Make preview calculate and return the price; save and notify only on explicit submitKeep the preview write but send the email silently in the backgroundCheck only that the preview price is correct and ignore database or email results

You can say this to an AI Agent

Separate quote preview from order submission: preview should calculate and return the price without writing a quote or sending email; only an explicit Confirm order should save and notify once. Add tests proving preview adds no record or email and one submission creates the expected external effects once.

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