blog/total-guide-to-jest-esm-and-angular

[giscus[bot]]

blog/total-guide-to-jest-esm-and-angular

Let's learn how to speed up our Angular Jest tests by more than 100% by switching to Jest ESM (a notoriously problematic migration) and how to solve all the troublesome issues that tend to pop up along the way!

https://angularexperts.io/blog/total-guide-to-jest-esm-and-angular

[timsar2]

From angular 16, ngcc was removed. Should we still using jest-preset-angular or there is a better way?

[sherlock1982]

You should still be using it as it provides a boilerplate. If you use jest without Angular CLI you will have to call setupZoneTestEnv from your test.ts. Otherwise don't call it

[eniomarku]

I am using angular version 16, which by default have under @angular/cdk only fesm2022. Should down-leveling to fesm2015 would work out of the box If there is no fesm2015 under my @angular/cdk directory?

[bhalperin]

Would highly appreciate an update to this blog, relevant to Angular 18 and Nx.
All my attempts to fix the dreaded message SyntaxError: Cannot use import statement outside a module have failed. I'm totally confused....
I'm using Angular 18 inside an Nx monorepo.

[raboud]

been fighting this and with angualar 18 and Nx for awhile....have you made any head way

[bhalperin]

Unfortunately not 😞

[sherlock1982]

It is worth mentioning the downsides of this migration. They're well described here https://jestjs.io/docs/ecmascript-modules. Specifically:

1. jest.mock won't work and you will have to mock via DI. That is bad if you highly rely on it
2. you will have to import from @jest/globals. This is even good as brings some extra type checking

Overall I don't fully understand why you mention the speed increase. You have to process all your ESM to CJS and by default you're using cache. So you process only once and there should be no noticable performance increase.

[sherlock1982]

From my experience - I tried it, fixed all jest.mock, interops e.t.c. Unfortunately I see that the memory of nodejs keeps growing until it crashes with OOM.
I don't see it if i run the same tests but with cjs