lib/testing/mixins.dart

abstract class Mixin1 {
  String get overriddenString => "mixin1";

  String get interfaceString;
  set interfaceString(String string);
  bool hasInterfaceString();
}

abstract class Mixin2 {
  String get overriddenString => "mixin2";

  bool hasOverriddenHasMethod() => false;
}

abstract class Mixin3 {}