private int count;
    private final AsyncFunction<X, V> delegate;

    public AsyncFunctionSpy(AsyncFunction<X, V> delegate) {
      this.delegate = delegate;
    }

    @Override
    public final ListenableFuture<V> apply(X t) throws Exception {
      count++;
      return delegate.apply(t);
    }

    void verifyCallCount(int expected) {

    private int count;
    private final AsyncFunction<X, V> delegate;

    public AsyncFunctionSpy(AsyncFunction<X, V> delegate) {
      this.delegate = delegate;
    }

    @Override
    public final ListenableFuture<V> apply(X t) throws Exception {
      count++;
      return delegate.apply(t);
    }

    void verifyCallCount(int expected) {