Using MockHero with Jest for Deterministic Test Fixtures

The Pattern

Generate test data once with a deterministic seed, save to __fixtures__/, and import from your Jest tests. No network calls on each run, but still realistic data.

// scripts/gen-fixtures.ts
import fs from "node:fs";

const data = await fetch("https://api.mockhero.dev/api/v1/generate", {
  method: "POST",
  headers: { "x-api-key": process.env.MOCKHERO_API_KEY!, "Content-Type": "application/json" },
  body: JSON.stringify({
    seed: 1,
    tables: [{
      name: "users", count: 20, fields: [
        { name: "id", type: "uuid" },
        { name: "email", type: "email" }
      ]
    }]
  })
}).then(r => r.json());

fs.writeFileSync("__fixtures__/users.json", JSON.stringify(data.users, null, 2));

// users.test.ts
import users from "../__fixtures__/users.json";

test("handles 20 users", () => {
  expect(users).toHaveLength(20);
});

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