matchAsync method

@override Future<String?> matchAsync(dynamic item)

Returns null if this matches item, or a String description of the failure if it doesn't match.

This can return a Future or a synchronous value. If it returns a Future, neither expect nor the test will complete until that Future completes.

If this returns a String synchronously, expect will synchronously throw a TestFailure and matches will synchronously return false.

Implementation

@override
Future<String?> matchAsync(dynamic item) async {
  // Cache the current goldenFileComparator so we can restore
  // it after the test.
  final originalComparator = goldenFileComparator;

  try {
    goldenFileComparator = PixelDiffGoldenComparator(
      (goldenFileComparator as LocalFileComparator).basedir.path,
      pixelCount: _maxPixelMismatchCount,
    );

    return await super.matchAsync(item);
  } finally {
    goldenFileComparator = originalComparator;
  }
}