public void AddCustomer()
{
//Arrange
var expectedFirstName = "John";
var expectedLastName = "Smith";
var expectedPhone = "1234567890";
int addSuccess = 1;
MainScreen form = new MainScreen();
var createControl = form.GetType().GetMethod("CreateControl", BindingFlags.Instance | BindingFlags.NonPublic);
createControl.Invoke(form, new object[] { true });
//Act - set up values
//result = 1 if new customer is added, result = 0 if customer can not be added
int actualResult = form.AddCustomer(expectedFirstName, expectedLastName, expectedPhone);
//Assertion - The expected output given the known inputs
Assert.Equal(addSuccess, actualResult);
}