Weird bug with Angular unit tests

[ms-dosx86]

Describe the bug

In the docs it says that in the unit tests we should await fixture.whenStable() so a query completes and we get its resulted data. It is true but if I add a class field that references to query.data the query's data becomes undefined.

Your minimal, reproducible example

https://github.com/ms-dosx86/test-when-stable

Steps to reproduce

1. Run ng test
2. See that the test passes
3. Uncomment the commented line in app.ts
4. Run the test again
5. Test fails

Expected behavior

I'm not sure what's going on there but I have a feeling that creating a class field that references to query.data shouldn't cause such behaviour.

How often does this bug happen?

Every time

Screenshots or Videos

No response

Platform

• MacOS 26.0.1 (25A362)
• Chrome 143.0.7499.193

Tanstack Query adapter

angular-query

TanStack Query version

5.90.22

TypeScript version

5.8.2

Additional context

No response

[eliellis]

I'm also having serious issues getting unit tests to work properly. There are a few other open issues that seem related to this:

• isSuccess() not triggering effect() during testing #9981
• Reading out query signals in template causes test failure #9910

If anyone has any insight–or has working examples of UTs using jest as the testing framework, I'd love to see them!

[benjavicente]

@ms-dosx86 your issue looks related to #7488

The current implementation of the proxy of query does not work, so for now you can do this instead

app = () => this.appQuery.data();

There, the proxy attribute accessor does not run on component initialization, fixing the issue.

[benjavicente]

@eliellis from my tests, it is a timing issue of the adapter. Some reproductions of those testing bugs can be fixed by doing

fixture.detectChanges()

// Sometimes, appRef.whenStable() is called just before it knwons it's unstable,
// so test can wait for js pending tasks to complete before with setTimeout
// await new Promise(resolve => setTimeout(resolve, 0));
// await new Promise(resolve => setTimeout(resolve, 0));

const appRef = TestBed.inject(ApplicationRef);
await appRef.whenStable();