func (w *MockDirectoryWrapper) _crash() error {
	w.crashed = true
	w.openFiles = make(map[string]int)
	w.openFilesForWrite = make(map[string]bool)
	w.openFilesDeleted = make(map[string]bool)
	files := w.unSyncedFiles
	w.unSyncedFiles = make(map[string]bool)
	// first force-close all files, so we can corrupt on windows etc.
	// clone the file map, as these guys want to remove themselves on close.
	m := make(map[io.Closer]error)
	for k, v := range w.openFileHandles {
		m[k] = v
	}
	for f, _ := range m {
		f.Close() // ignore error
	}

	for name, _ := range files {
		var action string
		var err error
		switch w.randomState.Intn(5) {
		case 0:
			action = "deleted"
			err = w.deleteFile(name, true)
		case 1:
			action = "zeroes"
			// Zero out file entirely
			var length int64
			length, err = w.FileLength(name)
			if err == nil {
				zeroes := make([]byte, 256)
				var upto int64 = 0
				var out store.IndexOutput
				out, err = w.BaseDirectoryWrapperImpl.CreateOutput(name, NewDefaultIOContext(w.randomState))
				if err == nil {
					for upto < length && err == nil {
						limit := length - upto
						if int64(len(zeroes)) < limit {
							limit = int64(len(zeroes))
						}
						err = out.WriteBytes(zeroes[:limit])
						upto += limit
					}
					if err == nil {
						err = out.Close()
					}
				}
			}
		case 2:
			action = "partially truncated"
			// Partially Truncate the file:

			// First, make temp file and copy only half this file over:
			var tempFilename string
			for {
				tempFilename = fmt.Sprintf("%v", w.randomState.Int())
				if !w.BaseDirectoryWrapperImpl.FileExists(tempFilename) {
					break
				}
			}
			var tempOut store.IndexOutput
			if tempOut, err = w.BaseDirectoryWrapperImpl.CreateOutput(tempFilename, NewDefaultIOContext(w.randomState)); err == nil {
				var ii store.IndexInput
				if ii, err = w.BaseDirectoryWrapperImpl.OpenInput(name, NewDefaultIOContext(w.randomState)); err == nil {
					if err = tempOut.CopyBytes(ii, ii.Length()/2); err == nil {
						if err = tempOut.Close(); err == nil {
							if err = ii.Close(); err == nil {
								// Delete original and copy bytes back:
								if err = w.deleteFile(name, true); err == nil {
									var out store.IndexOutput
									if out, err = w.BaseDirectoryWrapperImpl.CreateOutput(name, NewDefaultIOContext(w.randomState)); err == nil {
										if ii, err = w.BaseDirectoryWrapperImpl.OpenInput(tempFilename, NewDefaultIOContext(w.randomState)); err == nil {
											if err = out.CopyBytes(ii, ii.Length()); err == nil {
												if err = out.Close(); err == nil {
													if err = ii.Close(); err == nil {
														err = w.deleteFile(tempFilename, true)
													}
												}
											}
										}
									}
								}
							}
						}
					}
				}
			}
		case 3:
			// the file survived intact:
			action = "didn't change"
		default:
			action = "fully truncated"
			// totally truncate the file to zero bytes
			if err = w.deleteFile(name, true); err == nil {
				var out store.IndexOutput
				if out, err = w.BaseDirectoryWrapperImpl.CreateOutput(name, NewDefaultIOContext(w.randomState)); err == nil {
					if err = out.SetLength(0); err == nil {
						err = out.Close()
					}
				}
			}
		}
		if err != nil {
			return err
		}
		if VERBOSE {
			log.Printf("MockDirectoryWrapper: %v unsynced file: %v", action, name)
		}
	}
	return nil
}