public void Pushing_items_and_Popping_results_in_LIFO_action()
{
var stack = new MyStack();
stack.Push("1");
stack.Push("2");
stack.Push("3");
var result1 = stack.Pop();
var result2 = stack.Pop();
var result3 = stack.Pop();
Assert.AreEqual("3", result1);
Assert.AreEqual("2", result2);
Assert.AreEqual("1", result3);
}
public void Pushing_invalid_value_throws_error()
{
var stack = new MyStack();
Assert.ThrowsException <ArgumentException>(() => stack.Push(null));
}