Getting typeError: (options.astTransformers || []).map is not a function while running the test suite in Angular

This solution is for Angular 8/9/10

I would recommend doing these steps:

1. Uninstall jest-preset-angular
2. Reinstall jest-preset-angular
3. Clear jest cache
4. Retry

If the above solution not working, try installing

npm install --dev ts-jest

Jest configuration for Angular can be tricky.

I recommend you use jest-preset-angular which is a library that you will import into your Angular project that will manage the configuration of Jest for Angular.

This may be related to the update of Jest 27 that deprecated astTransformers as string[].

Configure your Angular project to use Jest 26 with jest-preset-angular and you should be fine