#include <iostream>
#include <algorithm>
#include <vector>

typedef long long ll;
typedef double lf;

// #define DEBUG 1
struct IO
{
    #define MAXSIZE (1 << 20)
    #define isdigit(x) (x >= '0' && x <= '9')
    char buf[MAXSIZE], *p1, *p2;
    char pbuf[MAXSIZE], *pp;
    #if DEBUG
    #else
    IO() : p1(buf), p2(buf), pp(pbuf) {}
    ~IO() {fwrite(pbuf, 1, pp - pbuf, stdout);}
    #endif
    #define gc() (p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, MAXSIZE, stdin), p1 == p2) ? ' ' : *p1++)
    #define blank(x) (x == ' ' || x == '\n' || x == '\r' || x == '\t')

    template <typename T>
    void Read(T &x)
    {
        #if DEBUG
        std::cin >> x;
        #else
        bool sign = 0; char ch = gc(); x = 0;
        for (; !isdigit(ch); ch = gc())
            if (ch == '-') sign = 1;
        for (; isdigit(ch); ch = gc()) x = x * 10 + (ch ^ 48);
        if (sign) x = -x;
        #endif
    }
    void Read(char *s)
    {
        #if DEBUG
        std::cin >> s;
        #else
        char ch = gc();
        for (; blank(ch); ch = gc());
        for (; !blank(ch); ch = gc()) *s++ = ch;
        *s = 0;
        #endif
    }
    void Read(char &c) {for (c = gc(); blank(c); c = gc());}

    void Push(const char &c)
    {
        #if DEBUG
        putchar(c);
        #else
        if (pp - pbuf == MAXSIZE) fwrite(pbuf, 1, MAXSIZE, stdout), pp = pbuf;
        *pp++ = c;
        #endif
    }
    template <typename T>
    void Write(T x)
    {
        if (x < 0) x = -x, Push('-');
        static T sta[35];
        int top = 0;
        do sta[top++] = x % 10, x /= 10; while (x);
        while (top) Push(sta[--top] ^ 48);
    }
    template <typename T>
    void Write(T x, char lst) {Write(x), Push(lst);}
} IO;
#define Read(x) IO.Read(x)
#define Write(x, y) IO.Write(x, y)
#define Put(x) IO.Push(x)

using namespace std;

const int MAXN = 2e5 + 10;

int n, ans, fr[MAXN], to[MAXN];
int m1, m2, tmp[MAXN];
vector <pair <int, int> > e[MAXN], res;
vector <int> pr[MAXN], cr, rem;

bool vis[MAXN], dir[MAXN], ind[MAXN];
bool b[MAXN];
int st[MAXN], top;
void DFS1(int u, int fa)
{
    st[++top] = u;
    vis[u] = 1;
    for (auto [v, w] : e[u])
        if (!vis[v]) ind[v] ^= 1, DFS1(v, u);
        else if (!dir[w] && v != fa) ind[v] ^= 1, pr[v].push_back(w), dir[w] = 1;
}
void DFS2(int u)
{
    for (auto [v, w] : e[u])
        if (!dir[w])
        {
            dir[w] = 1, DFS2(v), b[u] ^= b[v];
            if (b[v]) pr[u].push_back(w);
            else pr[v].push_back(w);
        }
}

inline void Solve(int u)
{
    top = 0, DFS1(u, 0);
    cr.clear();
    for (int i = 1; i <= top; i++)
        if (ind[st[i]]) cr.push_back(st[i]);
    for (int i = 0; i + 1 < cr.size(); i += 2) b[cr[i]] ^= 1, b[cr[i + 1]] ^= 1;
    DFS2(u);
}

int main()
{
    #if DEBUG
    #else
    ios::sync_with_stdio(0), cin.tie(0);
    #endif
    int T;
    Read(T);
    while (T--)
    {
        Read(n);
        for (int i = 1; i <= 2 * n; i++)
        {
            e[i].clear(), pr[i].clear();
            vis[i] = dir[i] = ind[i] = b[i] = 0;
        }
        for (int i = 1; i <= n * 2; i++) Read(fr[i]), Read(to[i]), tmp[i] = fr[i];
        sort(tmp + 1, tmp + n * 2 + 1), m1 = unique(tmp + 1, tmp + n * 2 + 1) - tmp - 1;
        for (int i = 1; i <= n * 2; i++) fr[i] = lower_bound(tmp + 1, tmp + m1 + 1, fr[i]) - tmp;
        for (int i = 1; i <= n * 2; i++) tmp[i] = to[i];
        sort(tmp + 1, tmp + n * 2 + 1), m2 = unique(tmp + 1, tmp + n * 2 + 1) - tmp - 1;
        for (int i = 1; i <= n * 2; i++) to[i] = lower_bound(tmp + 1, tmp + m2 + 1, to[i]) - tmp;
        for (int i = 1, u, v; i <= n * 2; i++)
        {
            u = fr[i], v = to[i];
            e[u].emplace_back(v + m1, i), e[v + m1].emplace_back(u, i);
        }
        for (int i = 1; i <= m1 + m2; i++)
            if (!vis[i]) Solve(i);
        rem.clear(), ans = 0, res.clear();
        for (int i = 1; i <= m1 + m2; i++)
        {
            ans += pr[i].size() / 2;
            for (int j = 0; j + 1 < pr[i].size(); j += 2)
                res.emplace_back(pr[i][j], pr[i][j + 1]);
            if (pr[i].size() & 1) rem.push_back(pr[i].back());
        }
        for (int i = 0; i + 1 < rem.size(); i += 2)
            res.emplace_back(rem[i], rem[i + 1]);
        cout << ans << '\n';
        for (auto [u, v] : res) cout << u << ' ' << v << '\n';
    }
    return 0;
}