public class MockVbeEvents
{
    public static Mock<IVBEEvents> CreateMockVbeEvents(Mock<IVBE> vbe)
    {
        var result = new Mock<IVBEEvents>();
        result.SetupReferenceEqualityIncludingHashCode();
        return result;
    }
}

        [Category("Code Explorer")]
        [Test]
        public void AddUserForm()
        {
            var builder = new MockVbeBuilder();
            var project = builder.ProjectBuilder("TestProject1", ProjectProtection.Unprotected)
                .AddComponent("Module1", ComponentType.StandardModule, "");

            var components = project.MockVBComponents;

            var vbe = builder.AddProject(project.Build()).Build();
            var vbeEvents = MockVbeEvents.CreateMockVbeEvents(vbe);

public RubberduckParserState(IVBE vbe, IProjectsRepository projectRepository, IDeclarationFinderFactory declarationFinderFactory, IVBEEvents vbeEvents)
        {
            _vbe = vbe ?? throw new ArgumentNullException(nameof(vbe));
            _projectRepository = projectRepository ?? throw new ArgumentException(nameof(projectRepository));
            _declarationFinderFactory = declarationFinderFactory ?? throw new ArgumentNullException(nameof(declarationFinderFactory));
            _vbeEvents = _vbeEvents ?? throw new ArgumentNullException(nameof(vbeEvents));

Dim subForm As Form_MySubForm

Set subForm = Me.MySubForm.Form
subForm.SomeControl.Value = 1

private void TreeView_OnMouseDoubleClick(object sender, MouseButtonEventArgs e)
        {
            if (ViewModel != null && ViewModel.OpenCommand.CanExecute(ViewModel.SelectedItem))
            {
                ViewModel.OpenCommand.Execute(ViewModel.SelectedItem);
            }
            e.Handled = true;
        }

Dim ctl As Access.Control
Dim sub As Access.SubForm

For Each ctl In Me.Controls
  If TypeOf ctl Is Access.SubForm
    Set sub = ctl
    ...
  End If
Next