public static async Task ShouldNotAddNode <TNode>(this IMixerViewModel mixer, IInteractionService interactions, INodeFactory nodeFactory, Func <IMixerViewModel, Task> command) where TNode : INode { // Arrange var isInvoked = false; interactions.GetNewNodePoint .RegisterHandler(i => { isInvoked = true; i.SetOutput(null); }); // Act mixer.Activator .Activate(); await command(mixer); // Assert isInvoked.Should().BeTrue(); nodeFactory.DidNotReceive().Create <TNode>(); mixer.Nodes.IsEmpty.Should().BeTrue(); }