Does a mock replace backend integration testing?

No. It accelerates frontend work and state coverage, but the real service still needs contract and integration testing.

Frontend development

Build the Frontend Before the Backend Is Ready

Create predictable mock REST endpoints for frontend development, including realistic data, CRUD, pagination, authentication, errors, and latency. Keep UI work moving against a local contract while the production service is still in development.

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Why does frontend work get blocked?

Screens are difficult to finish when the real API is unavailable, unstable, or missing important states. A contract-backed local mock gives the frontend a predictable target without pretending the production backend is complete.

Define the response contract first

Agree on serializable response shapes and resource paths, then capture them in exported TypeScript types. Both frontend code and the mock can work from the same field names and optionality.

TypeScript

interface Project {
  id: string;
  name: string;
  ownerId: string;
  status: "active" | "archived";
}

Use a repeatable frontend workflow

Create the project, bind resources, start the CLI, and set a development-only API base URL. Commit the contract and frontend behavior—not local tokens or SQLite data—to source control.

Environment

# .env.local
NEXT_PUBLIC_API_URL=http://localhost:4000

Exercise CRUD and nested resources

Use real GET, POST, PUT, PATCH, and DELETE requests against stateful local data. Configure parent-child resources when the UI navigates nested data such as customers and orders.

HTTP

GET /customers/customer-001/orders
PATCH /orders/order-041
content-type: application/json

{ "status": "shipped" }

Build pagination, search, and sorting UI

Match the planned query parameter names, endpoint page size, maximum limit, and sortable fields. The mock returns metadata and rejects invalid sort fields so the frontend can handle both success and validation states.

Test auth, loading, and failure states

Protect routes with bearer, API-key, or Basic authentication. Add fixed latency and probabilistic 503 failures to make loading, retry, session-expiry, and error components observable.

Switch to the real backend deliberately

Keep the API base URL configurable, validate the production service against the agreed contract, and run integration checks before switching. A mock reduces waiting and catches UI assumptions, but it cannot prove the production implementation matches.

Unblock the next screen

Start with the endpoint currently blocking the team and add only the behavior that screen needs. Expand the project as the shared contract develops.

Keep exploring

Last updated September 17, 2026. Product behavior described here is verified against the current Mock API Studio runtime.