Running test-storybook does not seem to see .stories.mdx files, only .stories.js files.

[KennethSlade]

When I run test-storybook, I only see my *.stories.js files get run and pass. I don't see any of my .stories.mdx files, even though stories are specified in main.js as both being valid:

module.exports = {
  stories: ["../src/**/*.stories.mdx", "../src/**/*.stories.@(js|jsx|ts|tsx)"],
...

Output looks like:

npm test

> my-storybook@0.5.2 test
> test-storybook --url http://localhost:4000

 PASS   browser: chromium  src/artifacts/xxxxxxx.stories.js
 PASS   browser: chromium  src/artifacts/yyyyyyy.stories.js

Test Suites: 2 passed, 2 total
Tests:       6 passed, 6 total
Snapshots:   0 total
Time:        5.024 s
Ran all test suites.

I have about 10 .stories.mdx files that aren't being picked up.

Am I missing a configuration option or something or is this a bug?