from collections import Counter
for _ in range(int(input())):
	n = int(input())
	s = input()
	freq = Counter(s)
	a = list()
	for x in freq.keys():
		a.append([freq[x], x])
	a.sort(reverse=True)
	ans = ['0']*n
	pos = 0
	for ct, c in a:
		while ct > 0:
			ans[pos] = c
			pos += 3
			if pos >= n:
				pos %= 3
				pos += 1
			ct -= 1
	good = 1
	for i in range(n-2):
		if ans[i] == ans[i+2]:
			if i+3 < n:
				ans[i+2], ans[i+3] = ans[i+3], ans[i+2]
	for i in range(n-1):
		if ans[i] == ans[i+1]:
			good = 0
		elif i+2 < n and ans[i] == ans[i+2]:
			good = 0
	if good == 0:
		print('NO')
	else:
		print('YES\n', ''.join(ans), sep='')