The class internal method call interceptor does not take effect

[raywang]

code like that

       // [MyCustomAttribute]
        public async Task TestAAsync(int id)
        {
            await TestBAsync(id);
        }
        [MyCustomAttribute]
        public async Task TestBAsync(int id)
        {
            await Task.Run(() =>
            {
                var abc = id;
            });

        }

Calling method TestAAsync from outside the class triggers the interceptor,This why?