Skip to main content

Test a Snap

You can test your Snap locally, in the Snaps sandbox, and end-to-end using Jest.

Test locally​

  1. Host your Snap locally:

    yarn start

  2. Install your Snap in Flask.

  3. Test your Snap by calling its API methods from a dapp.

Test in the sandbox​

Use the Snaps sandbox to test and debug your Snap in an easy-to-use interface.

  1. Run the sandbox subcommand to start the sandbox server:

    yarn mm-snap sandbox

    Navigate to the localhost URL displayed in the terminal.

  2. Install your Snap in Flask.

  3. Test your Snap by calling its API methods from the sandbox interface.

Test end-to-end​

Follow these steps to test your Snap end-to-end in a Jest environment.

1. Install @metamask/snaps-jest​

Install the @metamask/snaps-jest package into your Snap project using Yarn or npm:

yarn add -D @metamask/snaps-jest

or

npm i @metamask/snaps-jest

2. Configure @metamask/snaps-jest​

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

jest.config.js
module.exports = {
  preset: "@metamask/snaps-jest",
}

This automatically configures Jest to use the @metamask/snaps-jest environment, and to use the @metamask/snaps-jest matchers. You can then run the jest command as usual.

note

@metamask/snaps-jest assumes the Snap is built in the directory you run Jest from. If you use a different directory, you can specify the path using the server.root option, or by running your own HTTP server. It's currently not possible to use @metamask/snaps-jest with a Snap that is not built.

If you don't use the package as a preset, you can alternatively add the @metamask/snaps-jest environment and matchers to your Jest configuration manually:

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

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

jest.config.js
module.exports = {
  preset: "@metamask/snaps-jest",
  testEnvironmentOptions: {
    // Options go here.
  },
}

All options are optional.

3. Use @metamask/snaps-jest​

Use the package by calling any of the API methods. For example, you can:

You can also use Jest matchers to assert that a response from a Snap matches an expected value.

On this page