What is the right way to Moq Raise events for a C# Device Watcher Class?

I have a class which uses the DeviceWatcher class from Windows.Device.Enumeration:

Class A
{
   var temp = DeviceInformation.CreateWatcher(x,y,z);
   temp.Added += DoSomething;

   public void DoSomething(DeviceWatcher sender, DeviceInformation args)
   {
      //Do something;
   }
}

I want to unit test if Added event is called and DoSomething is invoked. My unit test looked like this:

class UnitTest{
    var mockDeviceWatcher = new Mock<DeviceWatcher>;
    this.A = this.container.Resolve<A>;
 }

However, I could not resolve Mock<DeviceWatcher> since it is a sealed class. As a work around, I created a facade class B and an interfaceB which is mockable:

class B
{
   private DeviceWatcher deviceWatcher;
   public event TypedEventHandler<DeviceWatcher, DeviceInformation> Added
    {
        add { this.deviceWatcher.Added += value; }
        remove { this.deviceWatcher.Added += value; }
    }  

}

I changed class A to use the facade class instead of the actual device watcher:

class A
{
   A(B facadeB)
   {
      facadeB.Added += DoSomething;
   }
   public void DoSomething(DeviceWatcher sender, DeviceInformation args)
   {
      //Do something;
   }
}

Now this helps me mock Device Watcher in the following way:

 class UnitTest{
      var mockDeviceWatcher = new Mock<IB>; //facade interface B
       this.A = this.container.Resolve<A>;
       mockDeviceWatcher.SetupAdd(m => m.Added += (sender, args) =>{});
       mockDeviceWatcher.Raise(m =>m.Added += (sender, args) => {});
       mockDeviceWatcher.Object.Added += (sender, args) =>{};
       mockDeviceWatcher.VerifyAdd(m =>m.Added +(sender, args) =>{});
  }

I get a test failure:

Expected invocation on the mock at least once but was never performed.

However, if I put breakpoints in DoSomething(), I can see them being hit, and if I replace the VerifyAdd with a VerifyAll, the test passes.

Question here:

1. ) Am I doing the right thing by using facade/wrappers?
2. ) Am I raising events in the right way to be tested?
3. ) Why does VerifyAll pass but VerifyAdd does not?