Solve the programming task below in a Python markdown code block.
You are given the sequence of Nucleotides of one strand of DNA through a string S of length N. S contains the character A, T, C, and G only.

Chef knows that:
A is complementary to T.
T is complementary to A.
C is complementary to G.
G is complementary to C.

Using the string S, determine the sequence of the complementary strand of the DNA.

------ Input Format ------ 

- First line will contain T, number of test cases. Then the test cases follow.
- First line of each test case contains an integer N - denoting the length of string S.
- Second line contains N characters denoting the string S.

------ Output Format ------ 

For each test case, output the string containing N characters - sequence of nucleotides of the complementary strand.

------ Constraints ------ 

$1 ≤ T ≤ 100$
$1 ≤ N ≤ 100$
$S$ contains A, T, C, and G only

----- Sample Input 1 ------ 
4
4
ATCG
4
GTCC
5
AAAAA
3
TAC

----- Sample Output 1 ------ 
TAGC
CAGG
TTTTT
ATG

----- explanation 1 ------ 
Test case $1$: Based on the rules, the complements of A, T, C, and G are T, A, G, and C respectively. Thus, the complementary string of the given string ATCG is TAGC.

Test case $2$: Based on the rules, the complements of G, T, and C are C, A, and G respectively. Thus, the complementary string of the given string GTCC is CAGG.

Test case $3$: Based on the rules, the complement of A is T. Thus, the complementary string of the given string AAAAA is TTTTT.

Test case $4$: Based on the rules, the complements of T, A, and C are A, T, and G respectively. Thus, the complementary string of the given string TAC is ATG.