Simplify @effect/vitest Test Effect API

[QuentinJanuel]

What is the problem this feature would solve?

At the moment, test effects in @effect/vitest are defined using the following pattern:

it.effect("message", () => someEffect)

Because someEffect is already a lazy computation, the arrow function feels redundant and does not simplify the developer experience.

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

Replace the current API with a direct call, removing the unnecessary arrow function:

it.effect("message", someEffect)

It would work on most cases, except when the function is actually used to pass an argument like in

it.effect.each(list)("message", item => someEffect)

but in these cases we could use an effect service like this:

it.effect.each(list)("message", E.gen(function* () {
  const item = yield* it.get // Consider a good naming here
  ...
}))

Furthermore, since all use cases I can think about would just use E.gen, we could streamline this further by requiring the generator function directly:

it.effect("message", function* () {
  // ...
})

I’m willing to implement this feature if it aligns with the project's direction. Before proceeding, I'd like to confirm whether this approach is desirable for @effect/vitest.

What alternatives have you considered?

No response

[mikearnaldi]

I kind of like:

it.effect("message", function* () {
  // ...
})

better than any alternative

[jessekelly881]

Don't forget test context. This might work well though.

it.effect("message", function* (ctx) {
  // ...
})

Or in the case of each or prop:

it.effect("message", function* (ctx, item) {
  // ...
})

[QuentinJanuel]

I don't know if having the test context as a parameter of the generator function is possible, and if so that might just be the cleanest indeed, but otherwise we can just provide a service to fetch it too

[mikearnaldi]

I don't know if having the test context as a parameter of the generator function is possible, and if so that might just be the cleanest indeed, but otherwise we can just provide a service to fetch it too

having it is indeed possible, what I am more worried about is instead pipeability, many times you need to add stuff like Effect.provide to the test.

Today with Effect.fn you can already do:

it.effect(
  "message",
  Effect.fn(function*(ctx) {
    ctx.expect(1).toBe(1)
  })
)

and piping would work like:

it.effect(
  "message",
  Effect.fn(
    function*(ctx) {
      ctx.expect(1).toBe(1)
    },
    Effect.timeout("1 second")
  )
)

if we were to support the generator directly we would need tons of overloads to support pipes

[mikearnaldi]

I don't know if having the test context as a parameter of the generator function is possible, and if so that might just be the cleanest indeed, but otherwise we can just provide a service to fetch it too

having it is indeed possible, what I am more worried about is instead pipeability, many times you need to add stuff like Effect.provide to the test.

Today with Effect.fn you can already do:

it.effect(
  "message",
  Effect.fn(function*(ctx) {
    ctx.expect(1).toBe(1)
  })
)

and piping would work like:

it.effect(
  "message",
  Effect.fn(
    function*(ctx) {
      ctx.expect(1).toBe(1)
    },
    Effect.timeout("1 second")
  )
)

if we were to support the generator directly we would need tons of overloads to support pipes

And also we would not have a place where to specify test config like:

it.effect(
  "message",
  Effect.fn(
    function*(ctx) {
      ctx.expect(1).toBe(2)
    },
    Effect.timeout("1 second")
  ),
  { fails: true }
)

If this becomes:

it.effect(
  "message",
   function*(ctx) {
     ctx.expect(1).toBe(2)
   },
   Effect.timeout("1 second")
)

Where would we put { fails: true }?

[QuentinJanuel]

Oh I didn't know about E.fn at all, this makes my suggestion feel way less interesting honestly
However it seems to me that E.fn first requires a name argument first and cannot be used like what you're describing. Am I missing something?

[QuentinJanuel]

Oh alright I just learnt it's a new variant that got released today