Unnecessary replication in jest.config.js files?

[adam-marshall]

Previously I added a moduleNameMapper value globally by adding it to jest.preset.js at the top level of the monorepo. This was to replace lodash-es imports with lodash, so it was better to add globally as lodash could be used anywhere.

The individual jest.config.js files for each lib do not contain any value for moduleNameMapper so it works globally.

However recently I had some pain trying to add a new snapshot serializer 'globally'.

My approach might be wrong here, but I added the snapshot serializer to jest.preset.js at the top level of the monorepo. This did not work because each jest.config.js file has the same 3 snapshot serializers (no-ng-attributes, ng-snapshot and html-comment), which means they do not use any snapshotSerializers on jest.preset.js, as that array overrides it.

If I delete the array on the individual jest.config.js files then my serializer is executed.

This does pose the question - I am no expert, but is there anything in the jest.config.js files which are generated per app and per lib, that could/should be configured for the whole monorepo instead?

[adam-marshall]

just to add to this, I just came across a scenario where I wanted to add something to setupFilesAfterEnv - I can't see any way of doing this globally.

each generated jest.config.js file overrides setupFilesAfterEnv with the path to test-setup so if I want to ensure something happens I have to manually change every test-setup file.

EDIT: it looks like if you add to the setupFilesAfterEnv array in jest.preset.js it can still figure out each path to test-setup.ts in each lib, and have global 'stuff' in it. - the individual setupFilesAfterEnv in each individual lib did not need to be deleted in this case, it uses the preset