Flush on TestOperation does not work if Query Document contains a Fragment

Describe the bug

The ApolloTestingController removes all flushed fields, which are described in a fragment.

To Reproduce

Having the following query:

query GetBenefitOptions {
  benefits {
    ...BenefitOption
  }
}

fragment BenefitOption on Benefit {
  __typename
  id
  description

  price {
    price
  }
}

and code in the component:

public readonly options$: Observable<BenefitOptionFragment[]> = this.getBenefitOptions.watch().valueChanges.pipe(
    map((result) => result.data.benefits),
    tap((val) => console.log(JSON.stringify(val)))
  );

I am doing the following test case:

// The change of the inputs should trigger the query
    const op: TestOperation<GetBenefitOptionsQuery> = controller.expectOne(GetBenefitOptionsDocument);

    // Mock the GraphQL response
    op.flushData({
      __typename: 'Query',
      benefits: [
        {
          __typename: 'PrivateBenefit',
          id: 'benefit-1' as BenefitID,
          description: 'Basic Cleaning',
          price: { price: 50 },
        },
        {
          __typename: 'PrivateBenefit',
          id: 'benefit-2' as BenefitID,
          description: 'Premium Cleaning',
          price: { price: 100 },
        },
        {
          __typename: 'PrivateBenefit',
          id: 'benefit-3' as BenefitID,
          description: 'Deep Cleaning',
          price: { price: 150 },
        },
      ],
    });

The component logs:

[{}, {}, {}]

Changing the query to not using a fragment

query GetBenefitOptions($filter: BenefitsFilterInput!) {
  benefits {
    __typename
    id
    description

    price {
      price
    }
  }
}

let the component produce the expected output

[{"__typename":"PrivateBenefit","id":"benefit-1","description":"Basic Cleaning","price":{"price":50}},{"__typename":"PrivateBenefit","id":"benefit-2","description":"Premium Cleaning","price":{"price":100}},{"__typename":"PrivateBenefit","id":"benefit-3","description":"Deep Cleaning","price":{"price":150}}]

Expected behavior

TestingController will also work with fragments.

Environment:

├── @angular/cli@18.2.12
├── @angular/core@18.0.5 overridden
├── @apollo/client@3.13.4
├── apollo-angular@10.0.3
├── graphql@16.9.0
└── typescript@5.4.4

Additional context

Using Karma to execute the tests.

Benefit is an interface.

Start with ApolloTestingController and TestOperation.flushData using the fragment-containing GetBenefitOptionsDocument shown in the reproduction. Run the relevant Karma tests around testing operations, then add a regression case for the BenefitOption fragment. Done means flushed fragment fields are preserved and the component receives the expected benefit objects instead of empty objects.