assertThrows and assertRejects: check properties of the thrown error other than message

[lionel-rowe]

Is your feature request related to a problem? Please describe.

For example, DOMExceptions with standardized name prop (but no standardized message prop):

// callback form `(err: E) => boolean`
assertRejects(() => new Promise((_, rej) => {
    const s = AbortSignal.timeout(0)
    s.onabort = () => rej(s.reason)
}), DOMException, (x) => x.name === 'TimeoutError')

Or custom error classes that don't use message:

class CustomError extends Error {
    readonly code: number
    constructor(code: number) {
        super()
        this.code = code
    }
}

// property bag form `{ [K in keyof E]: E[K] }`
assertThrows(() => {
    throw new CustomError(-1)
}, CustomError, { code: -1 })

Describe the solution you'd like

Allow checking properties of the thrown error other than message, e.g. with an optional errorCheck parameter.

Describe alternatives you've considered

• How does this argument fit into the current (overloaded) function signatures?
• Which form is better — callback, property bag, both, something else?
  • Callback is significantly more customizable (e.g. arbitrary checking of nested properties, more sophisticated checking of message prop such as exact match or regex match)
  • If supporting property bag, would need to decide how to check equality of nested data, possibly requiring an added dependency on assert/equal

[lionel-rowe]

I guess this would also needed to be added to assertIsError, so the param would be string | RegExp | ((err: E) => boolean) (and/or { [K in keyof E]: E[K] }).

[kt3k]

As discussed in #6629 (comment), the structure below is recommended way for doing additional assertions:

const e0 = assertThrows(...);
// do assertions about e0
const e1 = await assertRejects(...);
// do assertions about e1