class Class1 {
  int field;
  Class1(this.field);
  String toString() => 'Class1($field)';
}
class Class2 {
  int field;
  Class2(this.field);
  String toString() => 'Class2($field)';
}
extension on ;
Class1 (){ }
extension on ;
Class2 (){ }
main() { }
testExtension1() { }
testExtension2() { }
expect(expected, actual) { }