public void Push_ValidArg_AddTheObjectToTheStact()
{
var stact = new Stact <string>();
stact.Push("a");
Assert.That(stact.Count, Is.EqualTo(1));
}
public void Push_ArgIsNull_ThrowArgumentNullException()
{
var stact = new Stact <string>();
Assert.That(() => stact.Push(null), Throws.Exception.TypeOf <ArgumentNullException>());
}