---
title: Mock Tauri APIs
sidebar:
  order: 10
i18nReady: true
---

import SinceVersion from '../../../../components/SinceVersion.astro';

When writing your frontend tests, having a "fake" Tauri environment to simulate windows or intercept IPC calls is common, so-called _mocking_.
The [`@tauri-apps/api/mocks`] module provides some helpful tools to make this easier for you:

:::caution

Remember to clear mocks after each test run to undo mock state changes between runs! See [`clearMocks()`] docs for more info.

:::

## IPC Requests

Most commonly, you want to intercept IPC requests; this can be helpful in a variety of situations:

- Ensure the correct backend calls are made
- Simulate different results from backend functions

Tauri provides the mockIPC function to intercept IPC requests. You can find more about the specific API in detail [here][`mockipc()`].

:::note

The following examples use [Vitest], but you can use any other frontend testing library such as jest.

:::

### Mocking Commands for `invoke`

```javascript
import { beforeAll, expect, test } from "vitest";
import { randomFillSync } from "crypto";

import { mockIPC } from "@tauri-apps/api/mocks";
import { invoke } from "@tauri-apps/api/core";

// jsdom doesn't come with a WebCrypto implementation
beforeAll(() => {
  Object.defineProperty(window, 'crypto', {
    value: {
      // @ts-ignore
      getRandomValues: (buffer) => {
        return randomFillSync(buffer);
      },
    },
  });
});


test("invoke simple", async () => {
  mockIPC((cmd, args) => {
    // simulated rust command called "add" that just adds two numbers
    if(cmd === "add") {
      return (args.a as number) + (args.b as number);
    }
  });
});
```

Sometimes you want to track more information about an IPC call; how many times was the command invoked? Was it invoked at all?
You can use [`mockIPC()`] with other spying and mocking tools to test this:

```javascript
import { beforeAll, expect, test, vi } from "vitest";
import { randomFillSync } from "crypto";

import { mockIPC } from "@tauri-apps/api/mocks";
import { invoke } from "@tauri-apps/api/core";

// jsdom doesn't come with a WebCrypto implementation
beforeAll(() => {
  Object.defineProperty(window, 'crypto', {
    value: {
      // @ts-ignore
      getRandomValues: (buffer) => {
        return randomFillSync(buffer);
      },
    },
  });
});


test("invoke", async () => {
  mockIPC((cmd, args) => {
    // simulated rust command called "add" that just adds two numbers
    if(cmd === "add") {
      return (args.a as number) + (args.b as number);
    }
  });

  // we can use the spying tools provided by vitest to track the mocked function
  const spy = vi.spyOn(window.__TAURI_INTERNALS__, "invoke");

  expect(invoke("add", { a: 12, b: 15 })).resolves.toBe(27);
  expect(spy).toHaveBeenCalled();
});
```

To mock IPC requests to a sidecar or shell command you need to grab the ID of the event handler when `spawn()` or `execute()` is called and use this ID to emit events the backend would send back:

```javascript
mockIPC(async (cmd, args) => {
  if (args.message.cmd === 'execute') {
    const eventCallbackId = `_${args.message.onEventFn}`;
    const eventEmitter = window[eventCallbackId];

    // 'Stdout' event can be called multiple times
    eventEmitter({
      event: 'Stdout',
      payload: 'some data sent from the process',
    });

    // 'Terminated' event must be called at the end to resolve the promise
    eventEmitter({
      event: 'Terminated',
      payload: {
        code: 0,
        signal: 'kill',
      },
    });
  }
});
```

### Mocking Events

<SinceVersion version="2.7.0" />

There is partial support of the [Event System] to simulate events emitted by your Rust code via the `shouldMockEvents` option:

```javascript
import { mockIPC, clearMocks } from '@tauri-apps/api/mocks';
import { emit, listen } from '@tauri-apps/api/event';
import { afterEach, expect, test, vi } from 'vitest';

test('mocked event', () => {
  mockIPC(() => {}, { shouldMockEvents: true }); // enable event mocking

  const eventHandler = vi.fn();
  listen('test-event', eventHandler);

  emit('test-event', { foo: 'bar' });
  expect(eventHandler).toHaveBeenCalledWith({
    event: 'test-event',
    payload: { foo: 'bar' },
  });
});
```

`emitTo` and `emit_filter` are **not** supported yet.

## Windows

Sometimes you have window-specific code (a splash screen window, for example), so you need to simulate different windows.
You can use the [`mockWindows()`] method to create fake window labels. The first string identifies the "current" window (i.e., the window your JavaScript believes itself in), and all other strings are treated as additional windows.

:::note

[`mockWindows()`] only fakes the existence of windows but no window properties. To simulate window properties, you need to intercept the correct calls using [`mockIPC()`]

:::

```javascript
import { beforeAll, expect, test } from 'vitest';
import { randomFillSync } from 'crypto';

import { mockWindows } from '@tauri-apps/api/mocks';

// jsdom doesn't come with a WebCrypto implementation
beforeAll(() => {
  Object.defineProperty(window, 'crypto', {
    value: {
      // @ts-ignore
      getRandomValues: (buffer) => {
        return randomFillSync(buffer);
      },
    },
  });
});

test('invoke', async () => {
  mockWindows('main', 'second', 'third');

  const { getCurrent, getAll } = await import('@tauri-apps/api/webviewWindow');

  expect(getCurrent()).toHaveProperty('label', 'main');
  expect(getAll().map((w) => w.label)).toEqual(['main', 'second', 'third']);
});
```

[`@tauri-apps/api/mocks`]: /reference/javascript/api/namespacemocks/
[`mockipc()`]: /reference/javascript/api/namespacemocks/#mockipc
[`mockwindows()`]: /reference/javascript/api/namespacemocks/#mockwindows
[`clearmocks()`]: /reference/javascript/api/namespacemocks/#clearmocks
[vitest]: https://vitest.dev
[Event System]: /develop/calling-frontend/#event-system
