1. override
Future<String> generateForAnnotatedElement(Element element, EmbedTests annotation, BuildStep buildStep)

Source

@override
Future<String> generateForAnnotatedElement(
    Element element, EmbedTests annotation, BuildStep buildStep) async {
  if (path.isAbsolute(annotation.path)) {
    throw new Exception('must be relative path to the source file');
  }

  final String sourcePathDir = path.dirname(buildStep.input.id.path);

  final String filePath = path.join(sourcePathDir, annotation.path);

  if (!await FileSystemEntity.isFile(filePath)) {
    throw new Exception('Not a file! - $filePath');
  }

  final Map<String, String> content = _readFile(filePath);

  String result =
      'final Map<String, String> _\$${element.displayName}Tests = '
      '<String, String>{\n';
  content.forEach((String k, String v) {
    result += "r'''$k''': r'''$v''',\n";
  });
  result += '};\n';

  return result;
}