Why does ng test show errors in non-test files, but ng build doesn't?

When I run ng build, even with the --configuration production flag, I don’t get any compilation errors. However, when I run ng test, I see compilation errors in non-test files (component files), as shown in the screenshot.

Normally, such errors would also be highlighted by the IDE at the corresponding location, but in this case, they are only triggered and shown by ng test.

The issue first appeared after I migrated Angular from version 16 to 19 using the Angular Update Guide.

Any idea what might be causing this or how to investigate further?



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