Currently the utility class OutputAnalyzer can work with streams and process outputs.
I suggest adding a simple ctor that will help working with file:

  /**
   * Create an OutputAnalyzer, a utility class for verifying output and exit
   * value from a Process
   *
   * @param file a text file to analyze
   * @throws IOException If an I/O error occurs.
   */
  public OutputAnalyzer(File txt) throws IOException {
      this(new String(Files.readAllBytes(Paths.get(txt)));
  }