Jest ESM — Total Guide To More Than 100% Faster Testing For Angular⚡

#jest #testing #node #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!

TLDR;

Jest is fast until it isn't therefore we have to bother with ESM
Basic Jest ESM setup is pretty straight forward
There is an ideal Jest ESM scenario where it would just work if libraries implemented ESM correctly
In real life Jest ESM breaks because most libs ship incorrect ESM
The moduleNameMapper and transformIgnorePatterns are the main tools that will help is to fix all the Jest ESM problems
We're going to progress through list of common problems and their solutions (please share yours to make it more complete in the comments)

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