### Question:
GlusterFileSystem extends FileSystem { @Override public boolean isOpen() { return volptr > 0; }  @Override FileSystemProvider provider(); @Override void close(); @Override boolean isOpen(); @Override boolean isReadOnly(); @Override String getSeparator(); @Override Iterable<Path> getRootDirectories(); @Override Iterable<FileStore> getFileStores(); @Override Set<String> supportedFileAttributeViews(); @Override Path getPath(String s, String... strings); @Override PathMatcher getPathMatcher(String s); @Override UserPrincipalLookupService getUserPrincipalLookupService(); @Override WatchService newWatchService(); String toString();  }### Answer:
@Test public void testIsOpen_whenClosed() { fileSystem.setVolptr(-1); assertEquals(false, fileSystem.isOpen()); }
@Test public void testIsOpen_whenOpen() { assertEquals(true, fileSystem.isOpen()); }