How to assert a func to a type by reflect?

I am writing an RPC service in Go. I don't know how to convert a struct method to a Handler func.

What I tried:

type TestService struct{}

func (TestService) Foo(a int) error {
    return nil
}

type Handle func(a int) error

func TestHandle(t *testing.T) {
    ts := new(TestService)
    val := reflect.ValueOf(ts)
    // typ := reflect.TypeOf(ts)

    // fmt.Println(val.Method(0).Interface())
    // fmt.Println(val.Method(0).Type().ConvertibleTo(reflect.TypeOf(new(Handle))))

    switch reflect.Indirect(val).Method(0).Interface().(type) {
    case Handle:
        fmt.Println(" okokok " )
    default:
        fmt.Println(reflect.Indirect(val).Method(0).Type())
    }
}

But it fails. How should I do it?