jest.mock slows down tests a lot

[WojtekF]

🐛 Bug Report

mocking module import slows down tests execution a lot.

To Reproduce

I've produced minimal public repo as I've spotted the issue at my work and I can't share the code here. Simply create a class which imports to another classes, creates its instances and uses them. The simpler, the better. Then write tests for a given class with mocking class constructor. test execution takes aprox. 6 second.

Expected behavior

The tests are expected to run faster with mocked classes than usual code execution

Link to repl or repo (highly encouraged)

https://github.com/WojtekF/jest-mock-example

envinfo

System:
OS: Windows 10
CPU: (4) x64 Intel(R) Core(TM) i5-5200U CPU @ 2.20GHz
Binaries:
Node: 10.16.3 - C:\Program Files\nodejs\node.EXE
npm: 6.9.0 - C:\Program Files\nodejs\npm.CMD

[thymikee]

Why would you expect test to run faster with a mock of super simple function/class? Mocking is not free, unfortunately.

However, I'm pretty sure we could do something to make it faster, would you like to investigate?

[github-actions]

This issue is stale because it has been open for 1 year with no activity. Remove stale label or comment or this will be closed in 30 days.

[github-actions]

This issue was closed because it has been stalled for 30 days with no activity. Please open a new issue if the issue is still relevant, linking to this one.

[github-actions]

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.
Please note this issue tracker is not a help forum. We recommend using StackOverflow or our discord channel for questions.