One thing which is not clear to me in unit testing Pulumi infra is how to mimic an update of existing infra. How can I mimic in a unit test a certain state as starting point, create my infra and validate the proposed change set? Is it possible?

There’s no engine in the mocked unit tests, so there’s nobody to calculate that difference

Too bad, as that was one of the themes I documented in a slide deck which you might have seen circling internally at Pulumi.