| // @dart = 2.9 | 
 | class Class extends Superclass with Mixin {} | 
 |  | 
 | class Mixin { | 
 |   String method1(num argument1, num argument2) => "Mixin"; | 
 |   String method2(covariant int argument1, num argument2) => "Mixin"; | 
 |   String method3(num argument1, num argument2) => "Mixin"; | 
 |   String method4(covariant int argument1, int argument2) => "Mixin"; | 
 | } | 
 |  | 
 | class Superclass { | 
 |   String method1(num argument1, num argument2) => "Superclass"; | 
 |   String method2(num argument1, num argument2) => "Superclass"; | 
 |   String method3(num argument1, covariant int argument2) => "Superclass"; | 
 |   String method4(num argument1, covariant num argument2) => "Superclass"; | 
 | } | 
 |  | 
 | main() {} | 
 | void expect(expected, actual) {} | 
 | void throws(void Function() f) {} |