Importing ES modules in tests

[RossHathaway]

Hello. I am not sure why the require statement in test/test.js (const rollupStarterPlugin = require('..');
) works but other require statements don't.

Steps to reproduce issue:
clone repo
npm i
npm test (no problems)
create new file src/test-import.js containing export default 5
add to test/test.js const testImport = require('../src/test-import')
run npm test, get error "SyntaxError: Unexpected token 'export'" referring to export default 5 in src/test-import.js