Bug: Erroneous test setup due to the usage of contentChildren

[LukasMachetanz]

Description of the bug

Let's assume having a component SystemUnderTestComponent as the SUT. This component internally renders ActionsComponent, which will be mocked within the test setup. ActionsComponent uses the new API contentChildren for accessing its content children. Unfortunately this API causes problems for SystemUnderTestComponent as the following error is thrown: TypeError: Cannot read properties of undefined (reading 'Symbol(SIGNAL)').

An example of the bug

https://codesandbox.io/p/sandbox/competent-fermat-llrjgt?file=%2Fsrc%2Ftest.spec.ts%3A35%2C35

Expected behavior

I would expect that the tests of SystemUnderTestComponent are not influenced by internals of the mocked component ActionsComponent.

Maybe this behavior is caused by the fact that ActionsComponent is mocked and Angular can't find ActionComponent?