Recipe · Testing

Stable, seeded fake data for your tests

If your snapshot test asserts « Forged Hammer — €24.90 » and the fixture re-rolls tomorrow, the test fails for no reason. MockSmith generates data from a seed, so the same project returns the same records, run after run.

Updated June 7, 20264 min

Seeded by default

Generation runs through a seeded random generator tied to the project. The first record of products is the same string today, tomorrow and in CI. You assert on real values without hardcoding a live backend.

Stable order, too

Collections come back oldest-first, always in the same order. So data[0] in a paginated list is deterministic — perfect for « the first row should be… » assertions.

Tests that mutate — and clean up

Your tests POST, PATCH and DELETE against the mock, which changes its state. Two ways to keep runs isolated:

Undo what you write — delete the records your test created in a teardown step.
Scheduled reset (Pro) — have the project regenerate from its seed every hour or every day, wiping mutations back to the pristine dataset automatically.

A clean pattern

Read-only assertions

Assert on seeded GET data directly — it never changes.

Write in isolation

Use a dedicated project (or resource) for tests that create records.

Reset

Schedule a daily reset, or delete-on-teardown, so the next run starts clean.

vitest / jest

const base = "https://mocksmith.lioncore.dev/m/you/shop"; test("first product is stable", async () => {  const res = await fetch(`${base}/products?limit=1`);  const { data } = await res.json();  // deterministic: safe to snapshot  expect(data[0].name).toMatchSnapshot();});

Frequently asked

Is the data stable on the free plan?

Yes — seeding and stable ordering apply to every plan. Only the automatic scheduled reset is a Pro feature; on free you reset by re-generating manually or cleaning up in your tests.

If I regenerate the project, do I get the same data?

Yes, as long as the spec and seed are unchanged. Editing the spec (new field, different count) changes what's generated — intentionally.

Can I run tests in parallel against one mock?

Read-only tests, yes — concurrent GETs don't interfere. For write tests, isolate them (separate resources or projects) so they don't fight over the same records.

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How to mock a paginated REST API (no backend)

Build a fake REST endpoint with real pagination — page, limit, total and totalPages — and wire an infinite scroll against stable data.

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Mock an API with relations (foreign keys that hold)

Model users, posts and comments where every foreign key points to a record that actually exists — no dangling ids, no hand-wiring.

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