#!/usr/bin/env python3
import sys
import math
import random
import os
from io import BytesIO, IOBase

FAST_IO_BUFSIZE = 8192


class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._file = file
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, FAST_IO_BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()

    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, FAST_IO_BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")


sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip("\r\n")

class solution:
    lim = 2 * 10**6 + 5
    cache = {}

    def memoize(func):
        def memoizer(self, *args):
            if args not in self.cache:
                self.cache[args] = func(self, *args)
            return self.cache[args]
        return memoizer

    def __init__(self) -> None:
        pass

    def solve(self) -> None:
        t = int(input())
        for _ in range(t):
            self.solve_case(_)

    def solve_case(self, cs) -> None:
        n, k = map(int, input().split())
        num = input().strip()
        if k > n:
            raise ValueError("k > n")
        if k < 0:
            raise ValueError("k < 1")
        if n < 1:
            raise ValueError("n < 1")
        if n > 100:
            raise ValueError("n > 100")
        if k > 100:
            raise ValueError("k > 100")
        if n == k:
            print(0)
            return
        print(self.recur(num, k))
    
    @memoize
    def recur(self, num, k):
        if k == 0:
            return num
        ret = ''
        for i in range(0, len(num)):
            new_num = num[:i] + num[i+1:]
            ret = max(ret, self.recur(new_num, k - 1))
        return ret
        
if __name__ == "__main__":
    solution().solve()