#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,sse4.1,sse4.2,popcnt,mmx,avx")
using namespace std;
const int MOD = 1000000007;
const int UNDEF = -1;
const int INF = 1 << 30;
template <typename T>
inline bool chkmax(T &aa, T bb) {
  return aa < bb ? aa = bb, true : false;
}
template <typename T>
inline bool chkmin(T &aa, T bb) {
  return aa > bb ? aa = bb, true : false;
}
int rint();
char rch();
long long rlong();
const int mn = (2e5) + 4;
set<int> g[mn];
int dp[mn];
int dfs(int x) {
  if (dp[x] != -1) return dp[x];
  int ans = 0;
  for (auto &y : g[x]) {
    chkmax(ans, dfs(y) + 1);
  }
  return dp[x] = ans;
}
vector<int> d2x[mn];
char col[mn];
void solve(int n) {
  for (int d = n + 1; d >= 0; d--) {
    for (auto &x : d2x[d]) {
      if (col[x] == '?') {
        col[x] = 'R';
        for (auto &y : g[x]) {
          ;
          if (col[y] == '?') {
            col[y] = 'N';
          }
        }
      } else if (col[x] == 'N') {
        for (auto &y : g[x]) {
          col[y] = 'C';
        }
      }
    }
  }
}
void go() {
  int n, m;
  cin >> n >> m;
  for (int x = 0; x <= n + 1; x++) {
    g[x].clear();
    dp[x] = -1;
    d2x[x].clear();
    col[x] = '?';
  }
  for (int i = 1; i <= m; i++) {
    int x, y;
    cin >> x >> y;
    g[x].insert(y);
  }
  for (int x = 1; x <= n; x++) {
    d2x[dfs(x)].push_back(x);
  }
  solve(n);
  vector<int> vans;
  for (int x = 1; x <= n; x++)
    if (col[x] == 'C') vans.push_back(x);
  int num = vans.size();
  printf("%d\n", (int)vans.size());
  for (auto &ans : vans) printf("%d ", ans);
  printf("\n");
  if (num > (4 * n) / 7) {
    printf("%d %d\n", n, m);
    for (int x = 1; x <= n; x++)
      for (auto &y : g[x]) printf("%d %d\n", x, y);
    fflush(stdout);
    ;
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int t;
  cin >> t;
  for (int i = 0; i < t; i++) {
    go();
  }
}
static char stdinBuffer[1024];
static char *stdinDataEnd = stdinBuffer + sizeof(stdinBuffer);
static const char *stdinPos = stdinDataEnd;
void readAhead(size_t amount) {
  size_t remaining = stdinDataEnd - stdinPos;
  if (remaining < amount) {
    memmove(stdinBuffer, stdinPos, remaining);
    size_t sz = fread(stdinBuffer + remaining, 1,
                      sizeof(stdinBuffer) - remaining, stdin);
    stdinPos = stdinBuffer;
    stdinDataEnd = stdinBuffer + remaining + sz;
    if (stdinDataEnd != stdinBuffer + sizeof(stdinBuffer)) *stdinDataEnd = 0;
  }
}
int rint() {
  readAhead(16);
  int x = 0;
  bool neg = false;
  while (*stdinPos == ' ' || *stdinPos == '\n') ++stdinPos;
  if (*stdinPos == '-') {
    ++stdinPos;
    neg = true;
  }
  while (*stdinPos >= '0' && *stdinPos <= '9') {
    x *= 10;
    x += *stdinPos - '0';
    ++stdinPos;
  }
  return neg ? -x : x;
}
char rch() {
  readAhead(16);
  while (*stdinPos == ' ' || *stdinPos == '\n') ++stdinPos;
  char ans = *stdinPos;
  ++stdinPos;
  return ans;
}
long long rlong() {
  readAhead(32);
  long long x = 0;
  bool neg = false;
  while (*stdinPos == ' ' || *stdinPos == '\n') ++stdinPos;
  if (*stdinPos == '-') {
    ++stdinPos;
    neg = true;
  }
  while (*stdinPos >= '0' && *stdinPos <= '9') {
    x *= 10;
    x += *stdinPos - '0';
    ++stdinPos;
  }
  return neg ? -x : x;
}
