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Jest API and options

You can use the @metamask/snaps-jest package for end-to-end Snaps testing. This reference describes the available API methods, Jest matchers, and options.

API methods​

installSnap​

Installs a Snap in the execution environment. We recommend using this function in each test to ensure that it starts with a clean slate.

Parameters​

By default, if the built-in server is enabled, installSnap installs the Snap from the built-in server. Otherwise, you must specify a Snap ID to install.

Returns​

An object with functions that can be used to interact with the Snap.

Example​

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

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

request​

Sends a JSON-RPC request to the Snap.

Parameters​

A JSON-RPC request object with an addition optional origin property.

Returns​

A promise that resolves to the response from the onRpcRequest entry point, which can be checked using Jest matchers.

Example​

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

describe("MySnap", () => {
  it("should respond to foo with bar", async () => {
    const { request } = await installSnap(/* Optional snap ID */);
    const response = await request({
      origin: "http://localhost:8080",
      method: "foo",
      params: [],
    });

    /* Check the response using Jest matchers. Since the response is a standard JSON-RPC response,
     * you can use any standard Jest matchers to check it, including snapshot matchers. */
    expect(response).toRespondWith("bar");
    expect(response).not.toRespondWithError("baz");
    expect(response).toMatchSnapshot();
  });
});

onTransaction​

Sends a transaction to the Snap.

Parameters​

A transaction object with the following properties:

  • origin
  • chainId
  • from
  • to
  • value
  • data
  • gasLimit
  • maxFeePerGas
  • maxPriorityFeePerGas
  • nonce

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

Returns​

An object with the user interface that was shown by the Snap, in the onTransaction entry point.

Example​

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

describe("MySnap", () => {
  it("should return insights", async () => {
    const { onTransaction } = await installSnap(/* Optional Snap ID */);
    const response = await onTransaction({
      value: "0x0",
      data: "0x",
      gasLimit: "0x5208",
      maxFeePerGas: "0x5208",
      maxPriorityFeePerGas: "0x5208",
      nonce: "0x0",
    });
  
    expect(response).toRender(panel([text("Hello, world!")]));
  });
});

onCronjob​

Runs a cronjob in the Snap. The request is normally specified in the Snap manifest file under the endowment:cronjob permission, but this method allows you to run cronjobs that are not specified in the manifest as well.

Parameters​

A JSON-RPC request object.

Returns​

A promise that resolves to the response from the onCronjob entry point, which can be checked using Jest matchers.

Example​

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

describe("MySnap", () => {
  it("should end foo cronjobs with response bar", async () => {
    const { onCronjob } = await installSnap(/* Optional snap ID */);
    const response = await onCronjob({
      method: "foo",
      params: [],
    });

    // Check the response using Jest matchers.
    expect(response).toRespondWith("bar");
    expect(response).not.toRespondWithError("baz");
  });
});

onHomePage​

Requests the home page of the Snap. It takes no arguments, and returns a promise that resolves to the response from the onHomePage entry point.

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

describe("MySnap", () => {
  it("should render the home page", async () => {
    const { onHomePage } = await installSnap(/* Optional snap ID */);
    const response = await onHomePage();

    expect(response).toRender(panel([text("Hello, world!")]));
  });
});

getInterface​

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

Returns​

This method 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 } from "@metamask/snaps-jest";
import { text } from "@metamask/snaps-sdk";
import { assert } from "@metamask/utils";

describe("MySnap", () => {
  it("should render an alert with hello world", async () => {
    const { request } = await installSnap(/* Optional Snap ID */);

    // Note: You 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 infers the type of the user interface.
    assert(ui.type === "alert");
    expect(ui).toRender(text("Hello, world!"));

    // Select the OK button.
    await ui.ok();

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

Jest matchers​

@metamask/snaps-jest includes the following Jest matchers that you can use to assert that a response from a Snap matches an expected value:

  • toRespondWith(expectedResponse) - Checks if a response matches an expected response. This matcher checks the result property of the response. If the response is an error, this matcher fails.
  • toRespondWithError(expectedError) - Checks if a response matches an expected error. This matcher checks the error property of the response. If the response is not an error, this matcher fails.
  • toSendNotification(notificationText) - Checks if a Snap sent a notification.
  • toRender(expectedInterface) - Checks if a Snap rendered an interface. This is useful for testing the user interface of a Snap, either for a snap_dialog or a user interface rendered by the transaction insights API.

Options​

You can pass the following options when configuring @metamask/snaps-jest. All options are optional.

server​

Options for the built-in HTTP server included with this package. This server serves the execution environment, simulator, and the Snap bundle during tests.

The server options are:

  • enabled - Enables or disables the built-in HTTP server. Set to false to use your own HTTP server, which you can specify when calling installSnap, e.g. installSnap("local:http://my-server"). The default is true.
  • port - The port to use for the built-in HTTP server. The default is a random available (unprivileged) port.
  • root - The path to the root directory to serve the Snap files from. This is useful if you want to serve the Snap files from a different directory than the one Jest is running from. The default is the current working directory.

Example​

jest.config.js
module.exports = {
  preset: "@metamask/snaps-jest",
  testEnvironmentOptions: {
    server: {
      port: 8080,
      root: "/path/to/snap/files",
    },
  },
};