JSDoc @augments doesn’t allow function calls to augment existing types

I wrote a simple extension of [jest.Matchers][1] but I can not get the typescript type checker to recognize my extension. <!-- Please try to reproduce the issue with `typescript@next`. It may have already been fixed. --> **TypeScript Version:** 3.0.1 (and 3.1.0-dev.20180825) The description below is for 3.0.1 - for 3.1.0-dev.20180825 all jest functions show errors, so I don't even think that the parser gets to my type at all. ``` [ts] Cannot find name 'describe'. [ts] Cannot find name 'test'. [ts] Cannot find name 'expect ``` Used via vscode version: 1.26.1 <!-- Search terms you tried before logging this (so others can find this issue more easily) --> **Search Terms:** is:issue is:open jsdoc extends is:issue is:open jsdoc @augments is:issue is:open jsdoc "@augments" I first asked this as a [question on StackOverflow](https://stackoverflow.com/questions/51972275/jsdoc-document-object-method-extending-other-class) but after waiting a few days, I now suspect it is a bug in typescript's JSDoc implementation. I also read the FAQ and found [the link](https://github.com/Microsoft/TypeScript/wiki/FAQ#how-do-i-write-unit-tests-with-typescript) to jest but didn't find any information there either. I'm using plain JavaScript and the code runs perfectly. **Code** ```js // @ts-check const getFunctorValue = F => { let x F.fmap(v => x = v) return x } expect.extend({ /** * @extends jest.Matchers * @param {*} actual The functor you want to test. * @param {*} expected The functor you expect. */ functorToBe(actual, expected) { const actualValue = getFunctorValue(actual) const expectedValue = getFunctorValue(expected) const pass = Object.is(actualValue, expectedValue) return { pass, message () { return `expected ${actualValue} of ${actual} to ${pass ? '' : 'not'} be ${expectedValue} of ${expected}` } } } }) /** * @param {*} v Any value */ function just (v) { return { fmap: f => just(f(v)) } } describe('Functor …