CF2010A Alternating Sum of Numbers

You are given a sequence of integers. Output the alternating sum of this sequence. In other words, output $ a_1 - a_2 + a_3 - a_4 + a_5 - \dots $ . That is, the signs of plus and minus alternate, starting with a plus.

The first line of the test contains one integer $ t $ ( $ 1 \le t \le 1000 $ ) — the number of test cases. Then follow $ t $ test cases. The first line of each test case contains one integer $ n $ ( $ 1 \le n \le 50 $ ) — the length of the sequence. The second line of the test case contains $ n $ integers $ a_1, a_2, \dots, a_n $ ( $ 1 \le a_i \le 100 $ ).

**数据范围：** $1 \le t \le 1000$，$1 \le n \le 50$，$1 \le a_i \le 100$。