Allow for asserting throws on async methods

[mcgear]

We ran into a use case where we need to be able to assert throws from an async function. I was unable to figure out how to do this with existing assert throws, so added this implementation.

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[aapoalas]

You're probably looking for assertRejects

[iuioiua]

Aapo is right. See https://deno.land/std/assert/mod.ts?s=assertRejects

Perhaps we should mention the related asynchronous or synchronous function in each of the functions JSDocs. This isn't the first time someone hasn't realised one of these assertion functions exists.

[iuioiua]

@mcgear, please see the comments above.

[kt3k]

Perhaps we should mention the related asynchronous or synchronous function in each of the functions JSDocs. This isn't the first time someone hasn't realised one of these assertion functions exists.

Sounds good. Let's mention assertRejects in the doc of assertThrows

[mcgear]

This seems to have worked just fine, closing the PR.