ember-test-helpers: @ember/test-helpers@2 breaks build with mini-css-extract-plugin and ember-auto-import

We are using mini-css-extract-plugin and ember-auto-import to import styles from fullcalendar@5. The config looks like this:

    autoImport: {
      webpack: {
        plugins: [
          new MiniCssExtractPlugin({
            filename: 'vendor.css',
          }),
        ],
        module: {
          rules: [{
            test: /\.css$/,
            use: [MiniCssExtractPlugin.loader, 'css-loader'],
          }],
        },
      },
    },

It became possible after this was added to ember-auto-import https://github.com/ef4/ember-auto-import/pull/205

It was working fine so far.

I was trying to update our app to ember-qunit@5 and @ember/test-helpers@2. After doing the migration I’ve started getting the error:

ERROR in ../node_modules/@fullcalendar/daygrid/main.css
Module build failed (from ../node_modules/mini-css-extract-plugin/dist/loader.js):
ModuleBuildError: Module build failed (from ../node_modules/mini-css-extract-plugin/dist/loader.js):
Error: Didn't get a result from child compiler
...

If I remove @ember/test-helpers from the package.json the build starts working again. This is why I’m opening the issue against this repo, however, it might be something upstream.