Unit testing a component with Jest that imports a @smui component results in SyntaxError

[snowman-repos]

I'm trying to unit test my Svelte components using Jest. When those components import @smui components, running Jest throws an error:

SyntaxError: Cannot use import statement outside a module

Importing other node modules or other Svelte components runs fine. Running node v13.12.0. Have node-sass installed in node_modules.

The error seems to be caused by the first line import './_index.scss'; in node_modules/@smui/button/index.js.

Any ideas?

rollup.config.js

import resolve from '@rollup/plugin-node-resolve';
import replace from '@rollup/plugin-replace';
import commonjs from '@rollup/plugin-commonjs';
import svelte from 'rollup-plugin-svelte';
import postcss from 'rollup-plugin-postcss';
import babel from 'rollup-plugin-babel';
import { terser } from 'rollup-plugin-terser';
import config from 'sapper/config/rollup.js';
import pkg from './package.json';

const mode = process.env.NODE_ENV;
const dev = mode === 'development';
const legacy = !!process.env.SAPPER_LEGACY_BUILD;

const onwarn = (warning, onwarn) => (warning.code === 'CIRCULAR_DEPENDENCY' && /[/\\]@sapper[/\\]/.test(warning.message)) || onwarn(warning);
const postcssOptions = () => ({
  extensions: ['.scss', '.sass'],
  extract: false,
  minimize: true,
  use: [
    ['sass', {
      includePaths: [
        './src/theme',
        './node_modules',
      ]
    }]
  ]
});

export default {
	client: {
		input: config.client.input(),
		output: config.client.output(),
		plugins: [
			replace({
				'process.browser': true,
				'process.env.NODE_ENV': JSON.stringify(mode)
			}),
			svelte({
				dev,
				hydratable: true,
				emitCss: true
			}),
			resolve({
				browser: true,
				dedupe: ['svelte']
			}),
			commonjs(),

      postcss(postcssOptions()),

			legacy && babel({
				extensions: ['.js', '.mjs', '.html', '.svelte'],
				runtimeHelpers: true,
				exclude: ['node_modules/@babel/**'],
				presets: [
					['@babel/preset-env', {
						targets: '> 0.25%, not dead'
					}]
				],
				plugins: [
					'@babel/plugin-syntax-dynamic-import',
					['@babel/plugin-transform-runtime', {
						useESModules: true
					}]
				]
			}),

			!dev && terser({
				module: true
			})
		],

		onwarn,
	},

	server: {
		input: config.server.input(),
		output: config.server.output(),
		plugins: [
			replace({
				'process.browser': false,
				'process.env.NODE_ENV': JSON.stringify(mode)
			}),
			svelte({
				generate: 'ssr',
				dev
			}),
			resolve({
				dedupe: ['svelte']
			}),
			commonjs(),

      postcss(postcssOptions())
		],
		external: Object.keys(pkg.dependencies).concat(
			require('module').builtinModules || Object.keys(process.binding('natives'))
		),

		onwarn,
	},

	serviceworker: {
		input: config.serviceworker.input(),
		output: config.serviceworker.output(),
		plugins: [
			resolve(),
			replace({
				'process.browser': true,
				'process.env.NODE_ENV': JSON.stringify(mode)
			}),
			commonjs(),
			!dev && terser()
		],

		onwarn,
	}
};

jest.config.js

module.exports = {
  transform: {
    "^.+\\.svelte$": "jest-transform-svelte",
    "^.+\\.js$": "babel-jest",
  },
  moduleFileExtensions: ["js", "svelte"],
  testPathIgnorePatterns: ["node_modules"],
  bail: false,
  verbose: true,
  transformIgnorePatterns: ["node_modules"],
  setupFilesAfterEnv: ["@testing-library/jest-dom/extend-expect"],
};

babel.config.js

module.exports = {
  presets: [
    [
      "@babel/preset-env",
      {
        targets: {
          node: "current",
        },
      },
    ],
  ],
};

./src/components/Button.svelte (component to be tested)

<script>
  import Button from "@smui/button";
  export let text;
</script>

<button>{text}</button>

./tests/button.spec.js

import { render, cleanup } from "@testing-library/svelte";
import Button from "../src/components/Button.svelte";

describe("button component", () => {
  afterEach(() => {
    cleanup();
  }); // Default on import: runs it after each test.

  test("should render component correctly", () => {
    const test = "testing";

    const { container } = render(Button, {
      props: {
        text: test,
      },
    });

    expect(container).toContainHTML(`<button>${test}</button>`);
  });
});

Error when running jest tests

 ({"Object.<anonymous>":function(module,exports,require,__dirname,__filename,global,jest){import './_index.scss';
                                                                                             ^^^^^^

    SyntaxError: Cannot use import statement outside a module

      1 | <script type="module">
    > 2 |   import Button from "@smui/button";
        |                ^
      3 |   export let text;
      4 | </script>
      5 | 

      at Runtime.createScriptFromCode (node_modules/jest-runtime/build/index.js:1085:14)
      at Object.<anonymous> (src/components/Button.svelte:2:16)

Repo: https://github.com/darryl-snow/sapper-test

[snowman-repos]

In case anyone else faces the same issue, adding this to jest.config.js fixed it!

"moduleNameMapper": {
  "^.+\\.(css|less|scss)$": "babel-jest"
}