import java.io.; import java.util.; import java.util.stream.*;

class Result {

/*
 * Complete the 'happyLadybugs' function below.
 *
 * The function is expected to return a STRING.
 * The function accepts STRING b as parameter.
 */
public static String happyLadybugs(String b) {
    Map<Character, Integer> freq = new HashMap<>();
    boolean hasEmpty = false;

    for (char c : b.toCharArray()) {
        if (c == '_') {
            hasEmpty = true;
        } else {
            freq.put(c, freq.getOrDefault(c, 0) + 1);
        }
    }

    if (!hasEmpty) {
        for (int i = 0; i < b.length(); i++) {
            if ((i > 0 && b.charAt(i) == b.charAt(i - 1)) ||
                (i < b.length() - 1 && b.charAt(i) == b.charAt(i + 1))) {
                continue;
            }
            return "NO";
        }
        return "YES";
    }

    for (int count : freq.values()) {
        if (count == 1) {
            return "NO";
        }
    }

    return "YES";
}

}

public class Solution { public static void main(String[] args) throws IOException { BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in)); BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

    int g = Integer.parseInt(bufferedReader.readLine().trim());

    IntStream.range(0, g).forEach(gItr -> {
        try {
            int n = Integer.parseInt(bufferedReader.readLine().trim());
            String b = bufferedReader.readLine();
            String result = Result.happyLadybugs(b);
            bufferedWriter.write(result);
            bufferedWriter.newLine();
        } catch (IOException ex) {
            throw new RuntimeException(ex);
        }
    });

    bufferedReader.close();
    bufferedWriter.close();
}

}