class Child {
  #value: string;   

  get value(): string {
      return this.#value;
  }

  set value(newValue: string) {
    this.#value = newValue;
    // some other not relevant logic
  }
}

class Parent {
  constructor(private child: Child) {}

  someMethod() {
    this.someOtherMethod(this.child.value);
  }

  someOtherMethod(value: string) {
     // not relevant logic
  }
}

class MockChild implements Child {
  set value(value: string) {
     // empty setter
  }

  get value(): string {
     return ''; // In order not to break anything
  }
}

let value: jasmine.Spy;
let parent: Parent;
beforeEach(() => {
  const mockChild = new MockChild();
  value = spyOnProperty(mockChild, 'value', 'get')
  parent = new Parent(mockChild);
});

describe('method "someMethod"', () => {
  let someOtherMethod: jasmine.Spy;
  beforeEach(() => {
    someOtherMethod = spyOn(parent, 'someOtherMethod');
  });

  it('should call someOtherMethod with value from Child', () => {
    value.and.returnValue('some text');
    parent.someMethod();
    expect(someOtherMethod).toHaveBeenCalledWith('some text');
    expect(value).toHaveBeenCalledTimes(1);
  });
});