//add a delegate
public delegate void ItemClickedHandler(object sender, ItemClickedEventArgs e);
// add an event of the delegate type
public event ItemClickedHandler ItemClicked;

// не знаю, зачем весь этот геморрой - можно данные передавать в статическом объекте  ну да ладно
public class ItemClickedEventArgs : System.EventArgs
       {
           // add local member variables to hold object
           private Test test;
           // class constructor
           public ItemClickedEventArgs(Test _test)
           {
               this.test = _test;
           }
           // Properties - Viewable by each listener
           public Test TestInstance
           {
               get { return test; }
           }
       }

private void listViewSteps_Click(object sender, EventArgs e)
{
    if (listViewSteps.SelectedItems.Count > 1)
        return;
    Test selected_test = (listViewSteps.SelectedItems[0].Tag as Test);
    if (selected_test == null)
        return;
    SetTabControl(tabControlSettings, selected_test); 
    listViewSteps.LabelEdit = true;
    
    // instance the event args and pass a value
    ItemClickedEventArgs args = new ItemClickedEventArgs(selected_test);
    // raise the event with the updated arguments
    ItemClicked(this, args);
    this.Dispose();
}

 this.Dispose();

ItemClicked +=new ItemClickedHandler(ItemClicked);
ItemClicked(this, args);

 protected void OnItemClicked(ItemClickedEventArgs e)
 {
       var h = ItemClicked;
       if (h != null)
       {
           h(this, e);
       }
}

private void listViewSteps_Click(object sender, EventArgs e)
{
        // instance the event args and pass it each value
        ItemClickedEventArgs args = new ItemClickedEventArgs(selected_test);
        
       OnItemClicked(args);
} 

 private void MainForm_OnItemClicked(object sender, MainForm.ItemClickedEventArgs e)
 {
        textBoxTestName.Text = "Event Raised!!!";
}

MainForm.ItemClicked += MainForm_OnItemClicked;