#include <bits/stdc++.h>
using namespace std;
void solve() {
  long long n, k;
  cin >> n >> k;
  string ans = "";
  for (long long i = 0; i < n; i++) {
    ans.push_back('a');
  }
  for (long long i = n - 2; i >= 0; i--) {
    if (k <= n - i - 1) {
      ans[i] = 'b';
      ans[n - k] = 'b';
      break;
    }
    k -= (n - i - 1);
  }
  cout << ans << endl;
}
int main() {
  int t;
  cin >> t;
  while (t--) {
    solve();
  }
}
