### Question:
BlockStorage implements Closeable { public void merge( int mergeFactor, Cancellation cancellation ) throws IOException { monitor.mergeStarted( entryCount, calculateNumberOfEntriesWrittenDuringMerges( entryCount, numberOfBlocksInCurrentFile, mergeFactor ) ); File sourceFile = blockFile; File tempFile = new File( blockFile.getParent(), blockFile.getName() + ".b" ); try ( Allocator mergeBufferAllocator = bufferFactory.newLocalAllocator() ) { File targetFile = tempFile; ByteBuffer writeBuffer = mergeBufferAllocator.allocate( bufferFactory.bufferSize() ); ByteBuffer[] readBuffers = new ByteBuffer[mergeFactor]; for ( int i = 0; i < readBuffers.length; i++ ) { readBuffers[i] = mergeBufferAllocator.allocate( bufferFactory.bufferSize() ); } while ( numberOfBlocksInCurrentFile > 1 ) { try ( BlockReader<KEY,VALUE> reader = reader( sourceFile ); StoreChannel targetChannel = fs.open( targetFile, OpenMode.READ_WRITE ) ) { long blocksMergedSoFar = 0; long blocksInMergedFile = 0; while ( !cancellation.cancelled() && blocksMergedSoFar < numberOfBlocksInCurrentFile ) { blocksMergedSoFar += performSingleMerge( mergeFactor, reader, targetChannel, cancellation, readBuffers, writeBuffer ); blocksInMergedFile++; } numberOfBlocksInCurrentFile = blocksInMergedFile; monitor.mergeIterationFinished( blocksMergedSoFar, blocksInMergedFile ); } File tmpSourceFile = sourceFile; sourceFile = targetFile; targetFile = tmpSourceFile; } } finally { if ( sourceFile == blockFile ) { fs.deleteFile( tempFile ); } else { fs.deleteFile( blockFile ); fs.renameFile( tempFile, blockFile ); } } } BlockStorage( Layout<KEY,VALUE> layout, ByteBufferFactory bufferFactory, FileSystemAbstraction fs, File blockFile, Monitor monitor ); void add( KEY key, VALUE value ); void merge( int mergeFactor, Cancellation cancellation ); @Override void close();  }### Answer:
@Test void shouldMergeWhenEmpty() throws IOException { TrackingMonitor monitor = new TrackingMonitor(); int blockSize = 1_000; try ( BlockStorage<MutableLong,MutableLong> storage = new BlockStorage<>( layout, heapBufferFactory( blockSize ), fileSystem, file, monitor ) ) { storage.merge( randomMergeFactor(), NOT_CANCELLABLE ); assertEquals( 0, monitor.mergeIterationCallCount ); assertContents( layout, storage, emptyList() ); } }