🚀 Unit test should fail if an element is not known

Relevant Package

This feature request is for @angular/core.
And I think this is a kinda a regression since this behavior changed with Ivy.

Description

When executing unit tests with Karma and my test module has not been setup correctly, to contain all the relevant components, I get a warning like this:

WARN: ''app-my-element' is not a known element:
1. If 'app-my-element' is an Angular component, then verify that it is part of this module.
2. If 'app-my-element' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.'

The test is still successful in that case. In my opinion it should fail, since the test module clearly is missing this component.

I saw that there have been efforts to make it appear as an error: 00f3c58.
This has been reverted in this commit: 00f3c58.

But that wouldn't change the fact, that the test still passes.

Describe the solution you'd like

I would like one of these options:

• tests with unknown elements fail (as they did pre Ivy)
• an option to enable this behavior to make the tests fail
  • i.e. a CLI argument or a property in angular.json

If the default is "fail", then a user could add CUSTOM_ELEMENTS_SCHEMA or NO_ERRORS_SCHEMA to their test module if they want to suppress the errors.