Invalid Date object will throw a TypeError in Vitest

[dotnetCarpenter]

Describe the bug

The following two assertions should both succeed. But due to Vitest usage of .toJSON() on Date objects, the second line will fail with a TypeError.

expect(NaN).toBe(NaN);
expect(new Date('not a date')).toBe(NaN);

The reason is that .toJSON() returns undefined on invalid Date objects.

new Date('1990-01-01').toJSON();	// <- "1990-01-01T00:00:00.000Z"
new Date('foo bar').toJSON();		// <- null

On node 18.12 I get the following error:

TypeError: Cannot read properties of null (reading 'split')

On StackBlitz, I get:

TypeError: can't access property "split", dateObject.toJSON() is null

Reproduction

const { it, expect } = import.meta.vitest

it('Invalid Date is NaN', () => {
	expect (new Date ('not a date')).toBe (NaN)
})

System Info

System:
    OS: Linux 5.10 Ubuntu 22.04.1 LTS 22.04.1 LTS (Jammy Jellyfish)
    CPU: (4) x64 Intel(R) Core(TM) i7-4510U CPU @ 2.00GHz
    Memory: 2.22 GB / 3.83 GB
    Container: Yes
    Shell: 5.1.16 - /bin/bash
  Binaries:
    Node: 18.12.0 - /usr/local/bin/node
    Yarn: 1.22.18 - ~/.yarn/bin/yarn
    npm: 8.19.2 - /usr/local/bin/npm
  npmPackages:
    vite: ^3.2.0 => 3.2.0 
    vitest: ^0.24.3 => 0.24.3

Used Package Manager

npm

Validations

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[sheremet-va]

I think this is chai problem. The error comes from loupe package, according to stack trace. And is used by chai.

[dotnetCarpenter]

@sheremet-va I'm looking at package.json but I can not see Chai as a dependency. I do not know pnpm but I do see Chai in pnpm-lock.yaml. Sorry, this might not be important. I am only trying to understand when/why Chai is injected into Vitest, in order to better understand where a fix for invalid dates should exist. I do not think it is obvious that it should be fixed in Loupe.

Could you check out chaijs/loupe#58 and let us know what you think?

[sheremet-va]

I'm looking at package.json but I can not see Chai as a dependency

Not sure how you missed it: https://github.com/vitest-dev/vitest/blob/main/packages/vitest/package.json#L111

Vitest uses chai's expect with jest-compatible API.

Could you check out chaijs/loupe#58 and let us know what you think?

Not sure what I can say 😄 Your issue is correct, I would expect it to be fixed on their side, and then we just upgrade.

[dotnetCarpenter]

@sheremet-va This has been fixed in loupe 2.3.5 (npm).

After some lengthy discussions (chaijs/loupe#58 (comment), chaijs/loupe#59 (comment)), we settled on loupe returning "Invalid Date" for an invalid Date object. So the test code has changed slightly to:

const { it, expect } = import.meta.vitest

it('Invalid Date is "Invalid Date"', () => {
	expect (new Date ('not a date')).toBe ('Invalid Date')
})

[sheremet-va]

So the test code has changed slightly to

loupe only affects error messages.

You should not get the internal error, when you call expect(new Date('nod')).toBe(NaN), anymore. But you will still get an error, because toBe is using Object.is for equality check.

Correct check would be:

expect (new Date ('not a date').valueOf()).toBe(NaN)

Anyway, this issue can be closed, since Vitest 0.25.0 updated chai version to the one that has the fix.