TypeError: i is not a function

[joshnuss]

Describe the bug

Test fails with error message TypeError: i is not a function, and there is no stack trace displayed.

It appears the error is caused when a callback to a hook function (like beforeEach, beforeAll ) returns certain data types, like an array:

// TypeError: i is not a function
beforeEach(() => [])

// but this  is ok
beforeEach(() => Promise.resolve())

Reproduction

https://github.com/joshnuss/vitest-type-error-repro

System Info

System:
    OS: Linux 5.15 Linux Mint 20.3 (Una)
    CPU: (8) x64 Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
    Memory: 1.33 GB / 15.52 GB
    Container: Yes
    Shell: 5.0.17 - /bin/bash
  Binaries:
    Node: 16.15.1 - ~/.asdf/installs/nodejs/16.15.1/bin/node
    npm: 8.11.0 - ~/.asdf/plugins/nodejs/shims/npm
  Browsers:
    Chrome: 105.0.5195.52
    Firefox: 105.0
  npmPackages:
    vitest: ^0.23.4 => 0.23.4

Used Package Manager

pnpm

Validations

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• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[sheremet-va]

beforeEach expects a function to be returned: https://vitest.dev/api/#beforeeach

[joshnuss]

beforeEach seems to accept return values like null or Promise.

Two things:

• If other values aren't allowed, a better error message would be helpful.
• The error message didn't contain a stack trace, so it made it harder to debug the issue.

[sheremet-va]

beforeEach seems to accept return values like null or Promise.

cannot reproduce

If other values aren't allowed, a better error message would be helpful.

Agree

The error message didn't contain a stack trace, so it made it harder to debug the issue.

Stacktrace leads to internal implementations - we hide those, because otherwise throwing in a test will be bloated.

[joshnuss]

cannot reproduce

Maybe it's not reproducible with TS, but it is reproducible with JS.

Stacktrace leads to internal implementations - we hide those, because otherwise throwing in a test will be bloated

can you clarify? From a debugging perspective, if something went wrong while invoking beforeEach, it would be helpful to know where the error came from. Usually the stack trace helps with that kind of thing.

[sheremet-va]

if something went wrong while invoking beforeEach, it would be helpful to know where the error came from. Usually the stack trace helps with that kind of thing.

If something on your side is going wrong, you will see a stack trace to your code. Here the problem is with Vitest internals, so you don't see an error.

[jherdman]

This is definitely reproducible with TS. I hit the issue in converting a JS-based test to TS. What tripped me up was the Migration guide's recommendation for a done callback: https://vitest.dev/guide/migration.html. If you're not careful you end up with callback that the before hook doesn't like. Perhaps an assertion for the return type with a friendly error message would be useful?

[kswope]

Same problem here

I think this is hinted at in the docs: Awaitable.

Type: beforeEach(fn: () => Awaitable<void>, timeout?: number)

To be more clear

works

beforeEach(() => Promise.resolve())

doesn't

beforeEach(() => Promise.resolve("hi!"))

probably because of the cleanup function

beforeEach(() => Promise.resolve(() => console.log("cleaning up")))

So I guess Awaitable is either a promise wrapping a function or nothing?

Probably should check if the returned value is a function before it says incoherent things like "TypeError: i is not a function"

[joshnuss]

Thanks @sheremet-va!