docs: @VisibleForTesting
    static ImmutableList<Fact> formatExpectedAndActual(String expected, String actual) {
      ImmutableList<Fact> result;
  
      // TODO(cpovirk): Call attention to differences in trailing whitespace.
      // TODO(cpovirk): And changes in the *kind* of whitespace characters in the middle of the line.
  
      result = Platform.makeDiff(expected, actual);
      if (result != null) {
        return result;
      }
  
      result = removeCommonPrefixAndSuffix(expected, actual);
      if (result != null) {
        return result;
      }
  
      return ImmutableList.of(fact("expected", expected), fact("but was", actual));
    }