When using SinonJS in Typescript private properties are reported as missing

Question

I'm trying to stub a class instance using sinon.createStubInstance but I'm getting an error stating that a private member variable is missing. Of course I can't explicitly set it either because it's a private member.

Example classes:

class Foo {
  private readonly bar: string;

  constructor(bar: string) {
    this.bar = bar;
  }
}

class Parent {
  foos: Foo[];

  constructor(foos: Foo[]) {
    this.foos = foos;
  }
}

And in the test I'm writing a beforeEach block:

beforeEach(function () {
  const stubFoo = sinon.createStubInstance(Foo);

  const stubParent = sinon.createStubInstance(Parent);
  stubParent.foos = [stubFoo]; // Tslint error here
});

The Tslint error is:

Property 'bar' is missing in type 'SinonStubbedInstance' but required in type 'Foo'

For the record I'm using Typescript v3.0.3 and Sinon v7.4.1.

Answer 1

I personally like this solution found by a Github user (paulius-valiunas):

if you just want to use this in a couple places, a simpler and more readable solution would be to use the type alias StubbedClass<T> = SinonStubbedInstance<T> & T directly. For example:

export type StubbedClass<T> = SinonStubbedInstance<T> & T;
const myStub = sinon.createStubInstance(MyClass) as StubbedClass<MyClass>;

or just:

const myStub = sinon.createStubInstance(MyClass) as SinonStubbedInstance<MyClass> & MyClass;

way cleaner and simpler than other suggestions!