#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
  for (ll i = 0; i < v.size(); ++i) os << v[i] << " ";
  return os;
}
template <typename T>
ostream& operator<<(ostream& os, const set<T>& v) {
  for (auto it : v) os << it << " ";
  return os;
}
template <typename T, typename S>
ostream& operator<<(ostream& os, const pair<T, S>& v) {
  os << v.first << " " << v.second;
  return os;
}
const ll mod = 1e9 + 7;
const ll inf = 2e18;
const ll ninf = -2e18;
ll takemod(ll a) { return ((a % mod) + mod) % mod; }
ll pow(ll a, ll b, ll m) {
  ll ans = 1;
  a %= m;
  while (b) {
    if (b & 1) ans = (ans * a) % m;
    b /= 2;
    a = (a * a) % m;
  }
  return ans;
}
ll modinv(ll a) { return takemod(pow(takemod(a), mod - 2, mod)); }
void solve() {
  ll n, k;
  cin >> n >> k;
  if (k == 1) {
    for (ll i = 0; i < n - 2; i++) cout << "a";
    cout << "bb" << '\n';
    return;
  }
  ll i = 2;
  ll sum = 1;
  while (sum + i < k) {
    sum += i;
    i++;
  }
  ll req = k - sum;
  ll j = n - i - 1;
  ll lst = n - req;
  for (ll it = 0; it < n; it++) {
    if (it == j || it == lst)
      cout << "b";
    else
      cout << "a";
  }
  cout << '\n';
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  time_t t1, t2;
  t1 = clock();
  ll t;
  cin >> t;
  while (t--) solve();
  t2 = clock();
  cerr << '\n' << t2 - t1 << '\n';
  return 0;
}
