TestBed exists to configure Angular’s dependency injection and compile templates. If your test does neither, it is paying for both.

What to test how

• Services and pure logic: construct the class with plain objects for dependencies. No TestBed, no async, no fixtures.
• Component logic: with signals and standalone components, an instance can often be created directly and its methods called, which covers most of the interesting behaviour.
• Templates and interaction: TestBed, or better, a component harness that tests what a user can do rather than which class is present.

The gain is not only speed, although a suite going from four minutes to forty seconds changes whether people run it. It is that a test constructed without a framework fails for one reason, while a TestBed test can fail because of a missing provider in a module you did not write.