rc.2 Cannot configure the test module when the test module has already been instantiated

[LeonEck]

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

rc.1

Description

When switching from rc.1 to rc.2 I get a lot of these errors when running test with vitest and browser mode:

Cannot configure the test module when the test module has already been instantiated. Make sure you are not using `inject` before `TestBed.configureTestingModule`.

This is using vitest with "@vitest/browser-playwright": "4.0.8", and "options": { "browsers": ["chromium"] } set in the angular.json.

Minimal Reproduction

The errors are flaky, and each run produces a different amount. But I was able to get it to show up relatively reliably in a brand new (ng new) project (on rc.2) by making these changes:

• Install "@vitest/browser-playwright": "4.0.8",
• Add "options": { "browsers": ["chromium"] } to angular.json test config.
• Generate a second component and a service.
• Run ng test

In that setup, I get the error usually once or twice.

Exception or Error

Your Environment

Angular CLI       : 21.0.0-rc.2
Angular           : 21.0.0-rc.2
Node.js           : 24.11.1
Package Manager   : npm 11.6.2
Operating System  : darwin arm64

┌───────────────────────────┬───────────────────┬───────────────────┐
│ Package                   │ Installed Version │ Requested Version │
├───────────────────────────┼───────────────────┼───────────────────┤
│ @angular/build            │ 21.0.0-rc.2       │ 21.0.0-rc.2       │
│ @angular/cli              │ 21.0.0-rc.2       │ ^21.0.0-rc.2      │
│ @angular/common           │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ @angular/compiler         │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ @angular/compiler-cli     │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ @angular/core             │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ @angular/forms            │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ @angular/platform-browser │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ @angular/router           │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ rxjs                      │ 7.8.2             │ ~7.8.0            │
│ typescript                │ 5.9.3             │ ~5.9.2            │
│ vitest                    │ 4.0.8             │ ^4.0.8            │
└───────────────────────────┴───────────────────┴───────────────────┘

Anything else relevant?

No response

[LeonEck]

@clydin I can still reproduce the issue as described in the reproduction above, even with the changes from your PR.
I tried adding sequence: { setupFiles: 'list' }, to a vitest-base.config.ts, and I also tried editing the plugins.js file in node_modules directly. But even with this setting, I still get the error.

[clydin]

Reopening.
Please provide a minimal reproduction as we cannot otherwise reproduce the issue as described.

[clydin]

You can also try enabling test isolation via a custom runner configuration by running ng g config vitest and then adding isolate: true to the test section of vitest-base.config.ts. This may alleviate the issue for your project.

[LeonEck]

Here is a minimal reproduction: https://github.com/LeonEck/test-error
I added both isolate: true and sequence: { setupFiles: 'list' }, but running ng test still throws the error. Sometimes I only get it once, sometimes twice.

[clydin]

@LeonEck If possible, can you try the changes in here: #31792?

The issue appears to only represent itself when not in a headless mode but I was able to reproduce.

[LeonEck]

This still doesn't seem to 100% fix the issue. It is definitely better though. I can reproduce this with headless as well, it just need more tests. I added 20 services and 20 components to the reproduction: LeonEck/test-error@89cba9e
Using ng test --browsers chromiumheadless the error shows up in headless mode. Your patch does fix it for this simple reproduction. But in a real project of mine I still get like 1 or 2 instances of the error (but far fewer than before).

With this patch applied I also noticed that I get Cannot read properties of undefined (reading 'verify') as an error sometimes. This seems to refer to instances where we call .verify on an HttpTestingController instance within afterEach.

[LeonEck]

rc.3 seems to have fixed this. I can't reproduce it anymore.