TypeError: Jest: a transform must export something.

🐛 Bug Report

After upgrading from jest 23.6.3 to 27.0.1 and running our test suite we get the following error message:

TypeError: Jest: a transform must export something.

To Reproduce

1. Clone the GIT repo
2. Upgrade jest:

   name  range   from       to      url
>( ) jest  latest  26.6.3  ❯  27.0.1  https://jestjs.io/

1. Run yarn test

Expected behavior

No error message

Debug log:

# content of ts-jest.log :
{"context":{"allowJs":false,"logLevel":20,"namespace":"jest-preset","package":"ts-jest","version":"26.5.6"},"message":"creating jest presets not handling JavaScript files","sequence":1,"time":"2021-05-25T13:21:43.451Z"}
{"context":{"allowJs":false,"logLevel":20,"namespace":"jest-preset","package":"ts-jest","version":"26.5.6"},"message":"creating jest presets not handling JavaScript files","sequence":2,"time":"2021-05-25T13:21:43.474Z"}
{"context":{"logLevel":20,"namespace":"Importer","package":"ts-jest","version":"26.5.6"},"message":"creating Importer singleton","sequence":3,"time":"2021-05-25T13:21:45.906Z"}

envinfo

System:
    OS: Windows Server 2016
    Node version: 14.15.4

Npm packages:
    jest: 27.0.1
    ts-jest: 26.5.6
    typescript: 4.2.4

Related issue

[ahnpnl]

pls clear Jest cache and use ts-jest 27.0.0

[asohail-futu]

I used this: npx jest --clearCache which showed this message after running: Cleared /private/var/folders/mr/pkt42jm120gbnm9lddwm_n9cl2tb8h/T/jest_alc100 That seemed to have cleared the cache

adding to the previous comment – clearing the cache didn’t solve the issue for me. I’m still getting the original error mentioned in this thread.