Map<Path, Set<Integer>> changedLines() {
    return tracker.changedLines();
  }
@Test(expected = IllegalStateException.class)
  public void crash_on_invalid_start_line_format() throws IOException {
    String example = "Index: sample1\n"
      + "===================================================================\n"
      + "--- a/sample1\n"
      + "+++ b/sample1\n"
      + "@@ -1 +x1,3 @@\n"
      + " same line\n"
      + "+added line 1\n"
      + "+added line 2\n";

    printDiff(example);
    underTest.changedLines();
  }