# Mock (/docs/adapters/mock)



<ComponentPreview name="error-states" />

`mockAdapter` simulates throughput, latency, chunks, failures and resume, so you can
build and test every UI state before your backend exists.

```ts
import { MiB, UploadError, mockAdapter } from "@uploadcn/core"

const adapter = mockAdapter({
  speed: 2 * MiB,          // bytes per second
  latency: 250,            // ms before the first byte
  chunkSize: 5 * MiB,      // report chunk progress
  resumable: true,         // pause continues from the last byte
  failureRate: 0.1,        // 10% of attempts fail midway (retryable)
  fail: ({ file, attempt }) =>
    file.name.includes("forbidden")
      ? new UploadError("Forbidden", { code: "http", status: 403 })
      : null,
})
```

Results look like `{ key, url: "mock://uploads/…" }`.

## In tests [#in-tests]

The engine is plain TypeScript, so you can drive it from Vitest without a DOM:

```ts
const uploader = createUploader({ adapter: mockAdapter({ latency: 0, speed: 1e9 }), network: false })
const [item] = await uploader.add([new File(["hello"], "a.txt")])
await vi.waitFor(() => expect(uploader.getItem(item.id)?.status).toBe("success"))
```