### Question:
DelegateIncrementalFileMergerOutput implements IncrementalFileMergerOutput { @Override public void open() { delegate.open(); } DelegateIncrementalFileMergerOutput(@NonNull IncrementalFileMergerOutput delegate); @Override void open(); @Override void close(); @Override void remove(@NonNull String path); @Override void create(@NonNull String path, @NonNull List<IncrementalFileMergerInput> inputs); @Override void update(
            @NonNull String path,
            @NonNull List<String> prevInputNames,
            @NonNull List<IncrementalFileMergerInput> inputs);  }### Answer:
@Test public void open() { delegate.open(); Mockito.verify(mockOutput).open(); }