@CanIgnoreReturnValue
  public PathSubject containsLines(String... lines) throws IOException {
    return containsLines(Arrays.asList(lines));
  }
Asserts that the file is a regular file containing the given lines of text. By default, the
bytes are decoded as UTF-8; for a different charset, use {@link #withCharset(Charset)}.
jimfs/src/test/java/com/google/common/jimfs/PathSubject.java