Generic typing on custom plugins not working

[zbarbuto]

My example use case:

export const customTest = test.register('stubApi', stubApi);

function stubService<T>(service: T, method: keyof T, ...handlers) {
  return {
    run: () => {
      test.stub((<any>service).prototype, method, ...handlers);
    }
  };
}

class MyService {
  bar() { }
}
// I would expect this to type error since 'foo' does not exist on MyService
// however it works fine
customTest.stubService(MyService, 'foo', () => 'mock foo');

I'm unsure if it's something I'm doing wrong or not but you can't even apply a typing to stubService as you get "Expected 0 type arguments". I suspect it's something to do with the way plugins are registered.

Specifically, I think here: https://github.com/oclif/fancy-test/blob/master/src/types.ts#L49 that A extends any[] is not enough to infer Parameters<typeof stubService> as it should.