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I've seen these fail just by throwing errors

e.g. I was doing a POST to a rest api and it threw an auth error that showed up as a failed resource

You can throw an error indeed, see e.g. <https://github.com/pulumi/examples/blob/master/azure-ts-dynamicresource/cdnCustomDomain.ts#L164>

In fact, this is the way to let Pulumi know that a resource operation has failed; dynamic resource or not.

is there a way to test for throwing an error in an apply callback?

e.g.

```
const foo = someOutput.apply(value =&gt; {
    throw new Error("this will never resolve");
})
```

how would i assert the error or failure in my mocha tests?

<@UG77VR58X> hmm I am not sure how you could test if an error is thrown inside an `apply`. Have you looked at the blog post Joe did on unit testing? <https://blog.pulumi.com/testing-your-infrastructure-as-code-with-pulumi> …not sure if you did already, but perhaps something in there might provide a hint to something you could try.

I did read that blog post — I've based our tests on that — but did not find anything on catching errors thrown in apply

From the little I know about callback idioms, I think you'd provide an error handler as an argument to the apply?