### Question:
DelegateIncrementalFileMergerInput implements IncrementalFileMergerInput { @Override public void open() { delegate.open(); } DelegateIncrementalFileMergerInput(@NonNull IncrementalFileMergerInput delegate); @Override void open(); @Override void close(); @NonNull @Override ImmutableSet<String> getUpdatedPaths(); @NonNull @Override ImmutableSet<String> getAllPaths(); @NonNull @Override String getName(); @Nullable @Override FileStatus getFileStatus(@NonNull String path); @NonNull @Override InputStream openPath(@NonNull String path);  }### Answer:
@Test public void open() { delegate.open(); Mockito.verify(mockInput).open(); }