Why not hasReceived() or assertReceived()?

$repository->received('save')->with($book);

Read aloud, that line is already a sentence: "repository received save with book." That's not an accident — every verb in Double's API was picked to read this way. Which is exactly why the question comes up: hasReceived() and assertReceived() are the prefixes you'd expect from a testing library, so received() on its own can look like something's missing.

Nothing's missing. I'd rather give up a filler word — even if it leaves a slightly less complete-sounding English sentence — than let that word introduce ambiguity into what the code actually does.

One word, no strays

I gave a lot of thought to the terms used within Double. I wanted them to be one word, and I didn't want them to stray too far from the norm. expects, allows, received, verify are all common words within mocking libraries — nothing here is invented vocabulary.

Generally speaking, I tend not to use filler words anymore. They might make sense initially, but over time you realize they're often cost — extra characters — without benefit, especially in a typed language. You'll see this in Laravel: properties named hidden instead of isHidden. As a bool, is isn't adding much.

The filler word that creates ambiguity

Bringing it back to mocking libraries, these filler words can actually create ambiguity. Consider Mockery's shouldReceive:

shouldReceive — read as does, actually means can

Some people read should as does. But in fact it's closer to can — so, in Mockery, shouldReceive means "may or may not receive." This filler word might have led to the biggest misconception/misuse of Mockery.

does (certain) sits at one end, can (maybe) at the other — and should lands a lot closer to can than most people assume.

That's the failure mode a prefix invites: it reads as a claim about certainty, but it isn't one. received() doesn't have that problem, because it isn't claiming anything — it's just naming the fact you're checking. There's no tense or modal verb to misread, because there's no verb standing in front of the one that matters.