TEST(Deque, Can_Pop_Head_With_One_Element) {
  // Arrange
  Deque<int> deque;

  // Act
  const int N = 10;
  deque.push_Tail(N);

  // Assert
  EXPECT_EQ(N, deque.pop_Head());
}
TEST(Deque, Can_Push_Tail) {
  // Arrange
  Deque<int> deque;

  // Act
  const int N = 10;
  for (int i = 0; i < N; i++)
    deque.push_Tail(i);

  // Assert
  EXPECT_EQ(N, deque.Size());
}