private void assertDirectoryIsValid(File dir) {
    assertNotNull(dir);
    assertTrue(dir.exists());
    assertTrue(dir.canRead());
    assertTrue(dir.isDirectory());
  }
Asserts that the given directory is valid.
Checks -
1. Directory is not null
2. Directory exists
3. Directory is readable
4. Directory is a directory
@param dir the directory to check.
ambry-file-transfer/src/test/java/com/github/ambry/filetransfer/handler/StoreFileCopyHandlerIntegTest.java