#include <bits/stdc++.h>
using namespace std;

int intersection(pair<int, int>& a, pair<int, int>& b) {
  if (a.first > b.first) {
    swap(a, b);
  }

  if (a.second < b.first) {
    return 0;
  } else {
    return min(a.second, b.second) - b.first + 1;
  }
}

void solve() {
  int N, M;
  cin >> N >> M;
  string s;
  cin >> s;

  // prefix_value[i] = value after executing operations 0...i. (1 based indexing)
  // prefix_range[i] = range we've seen after executing operations 0..i
  // suffix_range[i] = range we've seen after executing operations i...N - 1.

  vector<int> prefix_value(N + 1, 0);
  vector<pair<int, int>> prefix_range(N + 1, { 0, 0 });
  int current = 0;
  for (int i = 1; i <= N; ++i) {
    const int v = (s[i - 1] == '+') ? 1 : - 1;
    current += v;
    prefix_value[i] = current;
    prefix_range[i].first = min(prefix_range[i - 1].first, current);
    prefix_range[i].second = max(prefix_range[i - 1].second, current);
  }

  vector<int> suffix_value(N + 1, 0);
  vector<pair<int, int>> suffix_range(N + 1, { 0, 0 });
  for (int i = N - 1; i >= 0; --i) {
    const int v = (s[i] == '+') ? 1 : - 1;
    suffix_value[i] = suffix_value[i + 1] + v;
    suffix_range[i].first = min(0, suffix_range[i + 1].first + v);
    suffix_range[i].second = max(0, suffix_range[i + 1].second + v);
  }

  for (int i = 0; i < M; ++i) {
    int left, right;
    cin >> left >> right;  // 1-based indexing.
    const int val = (left == 0) ? 0 : prefix_value[left - 1];
    pair<int, int> range_left = prefix_range[left - 1];
    pair<int, int> range_right = { val + suffix_range[right].first, val + suffix_range[right].second };
    // Join ranges.
    int num = (range_left.second - range_left.first + 1) + (range_right.second - range_right.first + 1);
    num -= intersection(range_left, range_right);
    cout << num << endl;
  }
}

int main() {
  int num_cases;
  cin >> num_cases;
  for (int i = 0; i < num_cases; ++i) {
    solve();
  }
}