If you know how to fix the issue, make a pull request instead.

• I tried using the @types/xxxx package and had problems.
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• Mention the authors (see Definitions by: in index.d.ts) so they can respond.
  • Authors: @davidparsson @borisyankov

If you do not mention the authors the issue will be ignored.

Consider the following cases.

interface Test {
  hello?: Function
}

const test: Test = {
  hello: () => {}
};

spyOn(test, 'hello'); 

will report type error, since hello can not be assigned to never.