Jimfs
An in-memory file system for Java 8+
...Jimfs supports most standard file operations, including file and directory creation, deletion, copying, symbolic and hard links, as well as stream-based file reading and writing. It also provides robust support for features like SecureDirectoryStream, WatchService for directory change notifications, and multiple attribute views (basic, posix, unix, dos, and acl). Users can configure Jimfs to mimic UNIX or Windows-style paths and behaviors, depending on the environment they need to simulate.