assert: add `expect()`

[cjihrig]

What is the problem this feature will solve?

expect() is a popular way of writing assertions. From what I've been able to tell, many developers prefer writing assertions in this style compared to the current assertion style provided by node:assert. Many batteries included test runners (Jest, Vitest, bun:test, etc.) expose this API.

What is the feature you are proposing to solve the problem?

node:assert exports the expect() API.

What alternatives have you considered?

Use the existing node:assert assertions or install expect() from npm.

[bakkot]

I think supporting two completely distinct styles of assertion in node core would be bad.

[cjihrig]

Not ideal, but I wouldn't say bad. The assert module is also pretty stable.

FWIW, this is a feature request that I'm making on behalf of the sheer number of people I've seen complain about the existing assertion style. I personally wouldn't use expect(), but I don't think we should ignore that most developers prefer it.

[bakkot]

It is definitely not my experience that most developers prefer it, but I agree a substantial number of developers do. I don't think we should add multiple ways to do the same thing whenever a substantial number prefers a different style than the existing one. That way lies madness.

[cjihrig]

That way lies madness.

That never stopped Node from adding strict assertions, Promise-based APIs, a few HTTP APIs, and other non-beautiful things in the past 😄

The thing about assert in particular is that a lot of it's APIs were added way back in the ~0.1 version days. For the longest time, we didn't even really support it being used by users. I don't think we should feel held back those types of ancient APIs, particularly when expect() would be a single API that can't really negatively interact with the existing ones.

Again, I'm just throwing this out there based on complaints I've seen. I don't really have a horse in this race.

[bakkot]

I agree that "the existing API is bad" (or incomplete) is a good reason to add a new one! I'm definitely not a minimalist. I just don't think the assert API actually is bad. It's pure stylistic preference.

[avivkeller]

I'm -1 on supporting a secondary assertion API. I think it makes more sense for a userland package to provide a compatibility layer for users who prefer expect over node:assert.

Adding this to core would effectively mean reimplementing something like Chai in Node.js, which seems unnecessarily redundant. If a user specifically needs an expect-style API instead of node:assert, there's also a good chance they need functionality beyond what node:assert provides, in which case they'd likely need a dependency anyway.