Angular 21 new unit test builder with Karma and zone.js

[szape89]

Command

test

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

20

Description

After upgrading from Angular 20 to 21, I ran into NGXXXX errors when running unit tests still with Karma and zone.js.
I found a closed issue and a supposed fix for it, but that did not resolve the issue.
Others experienced the same and implemented workarounds which actually do work: StackOverflow, Reddit.

I found that the solution could be that the angular.json has to be modified to be in line with the new project template like this:

• change "builder": "@angular/build:karma" to "builder": "@angular/build:unit-test"
• add "runner": "karma"
• remove the rest of the properties (according to documentation these derive from the development configuration)

I did not find anything regarding the necessity of this change in the documentation, but if that is the case, it would be wise to mention it and maybe even add a migration schematic.

Also its not clear what is the alternative for "main": "src/test.ts" which contains global test setup. My guess is that the "setupFiles" property would be the successor (like "karmaConfig" became "runnerConfig"), but that is disabled for Karma.

So my question is: Where should I put global test setup with the new "unit-test" builder when using Karma?

Thanks in advance.

Minimal Reproduction

npm test

Exception or Error

Your Environment

Angular CLI       : 21.2.5
Node.js           : 24.14.0
Package Manager   : npm 11.9.0
Operating System  : win32 x64

Anything else relevant?

No response