private Pair<List<File>, List<File>> createFilesAndDirsAtPath(File dir, int fileCount, int dirCount)
      throws IOException {
    List<File> createdFiles = new ArrayList<>();
    for (int i = 0; i < fileCount; i++) {
      File createdFile = new File(dir, "created-file-" + i);
      if (!createdFile.exists()) {
        assertTrue("Could not create " + createdFile, createdFile.createNewFile());
      }
      createdFile.deleteOnExit();
      createdFiles.add(createdFile);
    }
    List<File> createdDirs = new ArrayList<>();
    for (int i = 0; i < dirCount; i++) {
      File createdDir = new File(dir, "created-dir-" + i);
      assertTrue("Could not create " + createdDir + " now", createdDir.mkdir());
      createdDir.deleteOnExit();
      createdDirs.add(createdDir);
    }
    return new Pair<>(createdFiles, createdDirs);
  }
Creates {@code fileCount} files and {@code dirCount} directories at {@code dir}.
@param dir the directory to create the files and dirs at
@param fileCount the number of files to be created
@param dirCount the number of directories to be created
@return the list of files,dirs created as a pair.
@throws IOException
ambry-store/src/test/java/com/github/ambry/store/StorageManagerTest.java