retrofit-mock/src/main/java/retrofit2/mock/Calls.java
public static <T> Call<T> defer(Callable<Call<T>> callable) {
    return new DeferredCall<>(callable);
  }
public static <T> Call<T> defer(Callable<Call<T>> callable) {
    return new DeferredCall<>(callable);
  }
Invokes {@code callable} once for the returned {@link Call} and once for each instance that is
obtained from {@linkplain Call#clone() cloning} the returned {@link Call}.