Does vitest have the same problem as jest in this regard?

[spicylemonhaha]

When we analysed our customer’s tests, we soon noticed a recurring problem: that the most significant impact on performance was the number of modules which needed to be imported by the tests in question. Jest creates a new module registry for each test file and has to crawl through the whole dependency chain of modules which are imported by the test suite, even if they are completely unused. It is easy for developers to overlook this fact given that build tools such as webpack can eliminate dead code via tree-shaking, but this is only the case for production builds and does not help with test execution or development servers.

https://blog.codecentric.de/en/2021/11/javascript-test-performance-getting-the-best-out-of-jest/

[sheremet-va]

Yes, Vitest loads every imported module. It won't load a module, if imported variable is not used tho, which is a rare case and usually handled by linters.

I don't think tree-shaking is possible with Node.js context tho, we would need to bundle code for each test file.

[spicylemonhaha]

What do you use now to transform your code with Jest? If you are using Babel that is your answer. Babel is slow.

But both my jest and vitest are tested in the same environment and both have babel

[Demivan]

You used babel plugin for Vite? Because Vite uses esbuild by default.

[spicylemonhaha]

https://github.com/spicylemonhaha/test_example In this example, you will find that vitest performs better than jest (my environment is mac m1 pro)

[sheremet-va]

https://github.com/spicylemonhaha/test_example In this example, you will find that vitest performs better than jest (my environment is mac m1 pro)

According to your example, you don't use babel in Vitest. We use Vite to transform files, and it doesn't use babel, if not explicitly specified with vite-plugin-babel.

[spicylemonhaha]

I have now removed babel from the demo and changed the module syntax to commonjs (the reason why I use babel in jest is to use ESM), but vitest is still much faster than jest after testing, so what is the possible reason? , as far as I know jest is also multithreaded