@metamask/snaps-jest

@metamask/snaps-jest

A Jest preset for end-to-end testing MetaMask Snaps, including a Jest environment, and a set of Jest matchers.

• Installation
• Usage
  • Without the preset
• API
  • Install a snap
  • snap.request
  • snap.onTransaction
  • snap.onSignature
  • snap.onCronjob
  • snap.onHomePage
  • Jest matchers
  • Interacting with user interfaces
• Options

Installation

Use Node.js 16.0.0 or later. We recommend using nvm for managing Node.js versions.

Install a dependency in your snap project using yarn (or npm):

• yarn add -D @metamask/snaps-jest

Usage

The easiest way to use this package is to add it to your Jest configuration as a preset. In your jest.config.js file, add the following:

module.exports = {
  preset: '@metamask/snaps-jest',
};

This will automatically configure Jest to use the @metamask/snaps-jest environment, and to use the @metamask/snaps-jest matchers.

Then you can just run jest as usual.

Note: @metamask/snaps-jest assumes that the snap is built in the directory you're running Jest from. If you're using a different directory, you can specify the path to the snap using the root option, or by running your own HTTP server.

Right now it's not possible to use @metamask/snaps-jest with a snap that isn't built.

Without the preset

If you don't want to use the preset, you can still use the environment and matchers by adding them to your Jest configuration manually:

module.exports = {
  testEnvironment: '@metamask/snaps-jest',
  setupFilesAfterEnv: ['@metamask/snaps-jest/dist/cjs/setup.js'],
};

API

Install a snap

@metamask/snaps-jest exposes a installSnap function that can be used to install a snap in the execution environment. It's recommended to use this function in each test, to ensure that each test starts with a clean slate.

By default, if the built-in server is enabled, it will install the snap from the built-in server. Otherwise, you must specify a snap ID to install.

import { installSnap } from '@metamask/snaps-jest';

describe('MySnap', () => {
  it('should do something', async () => {
    await installSnap(/* optional snap ID */);
    // ...
  });
});

The installSnap function returns an object with functions that can be used to interact with the snap.

snap.request

The request function can be used to send a JSON-RPC request to the snap. It takes a single argument, which is similar to a JSON-RPC request object, but with an additional optional origin property. It returns a promise that resolves to the response from the onRpcRequest function.

import { installSnap } from '@metamask/snaps-jest';

describe('MySnap', () => {
  it('should do something', async () => {
    const { request } = await installSnap(/* optional snap ID */);
    const response = await request({
      origin: 'http://localhost:8080',
      method: 'foo',
      params: [],
    });
    // ...
  });
});

It returns an object with a response, and some additional metadata, which can be checked using the Jest matchers:

import { installSnap } from '@metamask/snaps-jest';

describe('MySnap', () => {
  it('should do something', async () => {
    const { request } = await installSnap(/* optional snap ID */);
    const response = await request({
      origin: 'http://localhost:8080',
      method: 'foo',
      params: [],
    });

    expect(response).toRespondWith('bar');
    expect(response).not.toRespondWithError('baz');
  });
});

Checking the response with standard Jest matchers

If you prefer, you can also manually check the response:

import { installSnap } from '@metamask/snaps-jest';

describe('MySnap', () => {
  it('should do something', async () => {
    const { request } = await installSnap(/* optional snap ID */);
    const { response } = await request({
      origin: 'http://localhost:8080',
      method: 'foo',
      params: [],
    });

    expect(response.result).toBe('bar');
    expect(response.error).toBeUndefined();
  });
});

Since the response is a standard JSON-RPC response, you can use any Jest matchers to check it, including snapshot matchers:

import { installSnap } from '@metamask/snaps-jest';

describe('MySnap', () => {
  it('should do something', async () => {
    const { request } = await installSnap(/* optional snap ID */);
    const { response } = await request({
      origin: 'http://localhost:8080',
      method: 'foo',
      params: [],
    });

    expect(response).toMatchSnapshot();
  });
});

snap.onTransaction

The onTransaction function can be used to send a transaction to the snap. It takes a single argument, which is an object with the following properties:

• origin: The origin of the transaction.
• chainId: The chain ID of the transaction.
• from: The address of the sender.
• to: The address of the recipient.
• value: The value of the transaction, in wei.
• data: The data of the transaction.
• gasLimit: The gas limit of the transaction.
• maxFeePerGas: The maximum fee per gas of the transaction.
• maxPriorityFeePerGas: The maximum priority fee per gas of the transaction.
• nonce: The nonce of the transaction.

All properties are optional, and have sensible defaults. The addresses are randomly generated by default. Most values can be specified as a hex string, or a decimal number.

It returns a getInterface function that gets the user interface that was shown by the snap, in the onTransaction function.

import { installSnap } from '@metamask/snaps-jest';
import { panel, text } from '@metamask/snaps-sdk';

describe('MySnap', () => {
  it('should do something', async () => {
    const { onTransaction } = await installSnap(/* optional snap ID */);
    const response = await onTransaction({
      value: '0x0',
      data: '0x',
      gasLimit: '0x5208',
      maxFeePerGas: '0x5208',
      maxPriorityFeePerGas: '0x5208',
      nonce: '0x0',
    });

    const screen = response.getInterface();

    expect(screen).toRender(panel([text('Hello, world!')]));
  });
});

snap.onSignature

The onSignature function can be used to send a signature request to the snap. It takes a single argument, which is an object with the following properties:

• origin: The origin of the signature request.
• from: The address of the signer.
• data: The data of the signature.
• signatureMethod: The signature method being used in the request.

All properties are optional, and have sensible defaults. The addresses are randomly generated by default. Most values can be specified as a hex string, or a decimal number.

It returns a getInterface function that gets the user interface that was shown by the snap, in the onSignature function.

import { installSnap } from '@metamask/snaps-jest';
import { panel, text } from '@metamask/snaps-sdk';

describe('MySnap', () => {
  it('should do something', async () => {
    const { onSignature } = await installSnap(/* optional snap ID */);
    const response = await onSignature();

    const screen = response.getInterface();

    expect(screen).toRender(
      panel([text('You are using the personal_sign method')]),
    );
  });
});

snap.onCronjob

The onCronjob function can be used to run a cronjob in the snap. It takes a single argument, which is similar to a JSON-RPC request object. It returns a promise that resolves to the response from the onCronjob function.

The request would normally be specified in the snap manifest under the endowment:cronjob permission, but this function allows you to run cronjobs that are not specified in the manifest as well.

import { installSnap } from '@metamask/snaps-jest';

describe('MySnap', () => {
  it('should do something', async () => {
    const { onCronjob } = await installSnap(/* optional snap ID */);
    const response = await onCronjob({
      method: 'foo',
      params: [],
    });
    // ...
  });
});

It returns an object with a response, and some additional metadata, which can be checked using the Jest matchers:

import { installSnap } from '@metamask/snaps-jest';

describe('MySnap', () => {
  it('should do something', async () => {
    const { onCronjob } = await installSnap(/* optional snap ID */);
    const response = await onCronjob({
      method: 'foo',
      params: [],
    });

    expect(response).toRespondWith('bar');
    expect(response).not.toRespondWithError('baz');
  });
});

snap.onHomePage

The onHomePage function can be used to request the home page of the snap. It takes no arguments, and returns a promise that contains a getInterface function to get the response from the onHomePage function.

import { installSnap } from '@metamask/snaps-jest';

describe('MySnap', () => {
  it('should do something', async () => {
    const { onHomePage } = await installSnap(/* optional snap ID */);
    const response = await onHomePage({
      method: 'foo',
      params: [],
    });

    const screen = response.getInterface();

    expect(screen).toRender(/* ... */);
  });
});

Jest matchers

@metamask/snaps-jest includes a set of Jest matchers that can be used to assert that a response from a snap matches an expected value:

• toRespondWith(expectedResponse): Check if a response matches an expected response. This matcher will check the result property of the response. If the response is an error, it will fail.
• toRespondWithError(expectedError): Check if a response matches an expected error. This matcher will check the error property of the response. If the response is not an error, it will fail.
• toSendNotification(notificationText): Check if a snap sent a notification.
• toRender(expectedInterface): Check if a snap rendered an interface. This is useful for testing the UI of a snap, either for a snap_dialog, UI rendered by the transaction insights API or the signature insights API.

Interacting with user interfaces

snap_dialog

If your snap uses snap_dialog to show user interfaces, you can use the request.getInterface function to interact with them. This method is present on the return value of the snap.request function.

It waits for the user interface to be shown, and returns an object with functions that can be used to interact with the user interface.

Example

import { installSnap, assertIsAlertDialog } from '@metamask/snaps-jest';
import { text } from '@metamask/snaps-sdk';
import { assert } from '@metamask/utils';

describe('MySnap', () => {
  it('should do something', async () => {
    const { request } = await installSnap(/* optional snap ID */);

    // Note: We cannot resolve the promise yet!
    const response = request({
      method: 'foo',
    });

    const ui = await response.getInterface();

    // This is useful if you're using TypeScript, since it will infer the type
    // of the user interface.
    assertIsAlertDialog(ui);
    expect(ui).toRender(text('Hello, world!'));

    // "Click" the OK button.
    await ui.ok();

    // Now we can resolve the promise.
    const result = await response;
    expect(result).toRespondWith('bar');
  });
});

handlers

If your snap uses handlers that shows user interfaces (onTransaction, onSignature, onHomePage), you can use the response.getInterface function to interact with them. This method is present on the return value of the snap.request function.

It returns an object with functions that can be used to interact with the user interface.

Example

import { installSnap } from '@metamask/snaps-jest';

describe('MySnap', () => {
  it('should do something', async () => {
    const { onHomePage } = await installSnap(/* optional snap ID */);
    const response = await onHomePage({
      method: 'foo',
      params: [],
    });

    const screen = response.getInterface();

    expect(screen).toRender(/* ... */);
  });
});

User interactions in user interfaces

The object returned by the getInterface function exposes other functions to trigger user interactions in the user interface.

• clickElement(elementName): Click on a button inside the user interface. If the button with the given name does not exist in the interface this method will throw.
• typeInField(elementName, valueToType): Enter a value in a field inside the user interface. If the input field with the given name des not exist in the interface this method will throw.

Example

import { installSnap } from '@metamask/snaps-jest';

describe('MySnap', () => {
  it('should do something', async () => {
    const { onHomePage } = await installSnap(/* optional snap ID */);
    const response = await onHomePage({
      method: 'foo',
      params: [],
    });

    const screen = response.getInterface();

    expect(screen).toRender(/* ... */);

    await screen.clickElement('myButton');

    const screen = response.getInterface();

    expect(screen).toRender(/* ... */);
  });
});

import { installSnap } from '@metamask/snaps-jest';

describe('MySnap', () => {
  it('should do something', async () => {
    const { onHomePage } = await installSnap(/* optional snap ID */);
    const response = await onHomePage({
      method: 'foo',
      params: [],
    });

    const screen = response.getInterface();

    expect(screen).toRender(/* ... */);

    await screen.typeInField('myField', 'the value to type');

    const screen = response.getInterface();

    expect(screen).toRender(/* ... */);
  });
});

Options

You can pass options to the test environment by adding a testEnvironmentOptions property to your Jest configuration. For example:

module.exports = {
  preset: '@metamask/snaps-jest',
  testEnvironmentOptions: {
    // Options go here.
  },
};

All options are optional, and have sensible defaults.

server

• Type: object

Options for the built-in HTTP server that is included with this package. This server is used to serve the execution environment, simulator, and the snap bundle during tests.

server.enabled

• Type: boolean
• Default: true

Whether to enable the built-in HTTP server. By default, it will be enabled. If you want to use your own HTTP server, you can disable this option, and use the executionEnvironmentUrl and simulatorUrl options to configure the URLs of your own server.

Example

module.exports = {
  preset: '@metamask/snaps-jest',
  testEnvironmentOptions: {
    server: {
      enabled: false,
    },
  },
};

server.port

• Type: number

The port to use for the built-in HTTP server. By default, it will use a random available (unprivileged) port.

Example

module.exports = {
  preset: '@metamask/snaps-jest',
  testEnvironmentOptions: {
    server: {
      port: 8080,
    },
  },
};

server.root

• Type: string
• Default: process.cwd()

The root directory to serve the snap files from. By default, it will use the current working directory. This is useful if you want to serve the snap files from a different directory than the one that Jest is running from.

Example

module.exports = {
  preset: '@metamask/snaps-jest',
  testEnvironmentOptions: {
    server: {
      root: '/path/to/snap/files',
    },
  },
};