private void assertExists(DirectoryEntry entry, String parent, String file) {
    assertThat(entry.exists()).isTrue();
    assertThat(entry.name()).isEqualTo(Name.simple(file));
    assertThat(entry.directory()).isEqualTo(files.get(parent));
    assertThat(entry.file()).isEqualTo(files.get(file));
  }
This path service is for unix-like paths, with the exception that it recognizes $ and ! as
roots in addition to /, allowing for up to three roots. When creating a {@linkplain
PathType#toUriPath URI path}, we prefix the path with / to differentiate between a path like
"$foo/bar" and one like "/$foo/bar". They would become "/$foo/bar" and "//$foo/bar"
respectively.
jimfs/src/test/java/com/google/common/jimfs/FileTreeTest.java