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Tomas Trajan 🇨🇭 for Angular

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


  • 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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