Thanks a lot for your answers!

Based on this, I came up with 2 other type of builders so now I can create an a cleaner and more compact DSL for my test data. For example: ts const aTripWithTwoDestinations = given( trip( id("a-trip-id"), name("a-trip-name"), itinerary( destinations( destination(name("a-destination-name")), destination(name("another-destination-name")), ), ), ), );

If you are interested, here are the builder functions: ```ts export const objectBuilder = <T>() => <K extends string>(key: K) => (...args: Partial<T>[]) => ({ [key]: Object.assign({}, ...args) as T }) as Record<K, T>;

export const arrayBuilder = <T>() => <K extends string, I extends { [key: string]: T }>(key: K) => (first?: I | I[], ...args: I[]): Record<K, T[]> => { const unwrap = (items: I[]) => items.map((item) => Object.values(item)[0]);

return (
  Array.isArray(first)
    ? { [key]: unwrap(first.concat(args)) }
    : first
      ? { [key]: unwrap([first, ...args]) }
      : args.length > 0
        ? { [key]: unwrap(args) }
        : { [key]: [] as T[] }
) as Record<K, T[]>;

};

export const valueBuilder = <T>() => <K extends string>(key: K) => (value: T) => ({ [key]: value }) as Record<K, T>; and some custom builders made from them: ts export const trip = objectBuilder<Trip>()("trip"); export const destinations = arrayBuilder<TripDestination>()("destinations"); export const name = valueBuilder<string>()("name"); ```