#include<bits/stdc++.h>
#define endl        '\n'
#define F           first
#define S           second
#define pb          push_back
#define yes         cout<<"YES\n"
#define no          cout<<"NO\n"
#define all(x)      x.begin(),x.end()
#define allr(x)     x.rbegin(),x.rend()
#define error1(x)   cerr<<#x<<" = "<<(x)<<endl
#define error2(a,b) cerr<<"("<<#a<<", "<<#b<<") = ("<<(a)<<", "<<(b)<<")\n";
#define coutall(v)  for(auto &it: v) cout << it << " "; cout << endl;
using namespace std;
using ll = long long;
using ld = long double;

void solve() {
    ll n, m;
    string s1;
    cin >> n >> m >> s1;
    
    // cerr << n << " " << m << " " << s1 << endl;
    string ans = s1, s2 = s1;
    sort(all(s2));

    if(n <= m + 1) {
        cout << s2 << endl;
        return;
    }
    
    auto rec = [&](auto&& self, string s, int i, ll k) -> void {
        if(i == n or k == 0) {
            ans = min(ans, s);
            return;
        }
        if(s[i] == s2[i]) {
            self(self, s, i + 1, k);
        }
        else {
            for(int j = i + 1; j < n; j++) {
                if(s[j] == s2[i]) {
                    swap(s[i], s[j]);
                    self(self, s, i + 1, k - 1);
                    swap(s[i], s[j]);
                }
            }
        }
        return;
    };

    rec(rec, s1, 0, m);
    cout << ans << endl;

    return;
}

int main() {
    ios::sync_with_stdio(false); cin.tie(0);
    int tc = 1;
    cin >> tc;
    for (int t = 1; t <= tc; t++) {
        // cout << "Case " << t << ": ";
        solve();
    }
    return 0;
}