// #pragma comment(linker, "/stack:200000000")
// #pragma GCC optimize("Ofast,no-stack-protector")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
// #pragma GCC optimize("unroll-loops")

#include <stdio.h>
#include <bits/stdc++.h>

#ifdef PERVEEVM_LOCAL
    #define debug(x) std::cerr << (#x) << ":\t" << (x) << std::endl
#else
    #define debug(x) 238
#endif

#define fastIO std::ios_base::sync_with_stdio(false); std::cin.tie(0); std::cout.tie(0)
#define NAME "File"

using ll = long long;
using ld = long double;

#ifdef PERVEEVM_LOCAL
    std::mt19937 rnd(238);
#else
    std::mt19937 rnd(std::chrono::high_resolution_clock::now().time_since_epoch().count());
#endif

template<typename T1, typename T2>
std::ostream& operator<<(std::ostream& out, const std::pair<T1, T2>& p) {
    out << "(" << p.first << ", " << p.second << ")";
    return out;
}

template<size_t index, typename T>
std::ostream& print_tuple(std::ostream& out, const T& t) {
    if constexpr (index == std::tuple_size<T>::value) {
        out << ")";
        return out;
    } else {
        if (index > 0) {
            out << ", ";
        } else {
            out << "(";
        }
        out << std::get<index>(t);
        return print_tuple<index + 1, T>(out, t);
    }
}

template<typename ...T>
std::ostream& operator<<(std::ostream& out, const std::tuple<T...>& t) {
    return print_tuple<0, std::tuple<T...>>(out, t);
}

template<typename Container, typename = decltype(std::begin(std::declval<Container>()))>
typename std::enable_if<!std::is_same<Container, std::string>::value, std::ostream&>::type
operator<<(std::ostream& out, const Container& container) {
    out << "{";
    for (auto it = container.begin(); it != container.end(); ++it) {
        if (it != container.begin()) {
            out << ", ";
        }
        out << *it;
    }
    out << "}";
    return out;
}

template<typename T>
bool smin(T& a, const T& b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}

template<typename T>
bool smax(T& a, const T& b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

const double PI = atan2(0.0, -1.0);
const int INF = 0x3f3f3f3f;
const ll LINF = (ll)2e18;
const int N = 500100;

int a[N], b[N];

void solve() {
	int n, m;
	scanf("%d%d", &n, &m);

	ll ans = 0;
	std::vector<std::pair<int, int>> diff;
	for (int i = 0; i < n; ++i) {
		scanf("%d%d", &a[i], &b[i]);
		ans += a[i];
		diff.emplace_back(b[i] - a[i], i);
	}

	if (n == 1) {
		printf("%d\n", b[0]);
		return;
	}

	std::sort(diff.rbegin(), diff.rend());

	// debug(ans);

	int prefSize = n;
	int curCan = m - 1;
	for (auto[curDiff, i] : diff) {
		// debug(curDiff);
		// debug(i);
		// debug(prefSize);
		// debug(curCan);
		if (curDiff < 0) {
			break;
		}
		if (curCan - 1 < prefSize - 1) {
			break;
		}

		if (prefSize == 2) {
			int lastDiff = diff.back().first;
			if (curDiff + lastDiff > 0) {
				ans += curDiff + lastDiff;
			}
			break;
		}

		ans += curDiff;
		curCan -= 2;
		--prefSize;
	}

	printf("%lld\n", ans);
}

void run() {
	int t;
	scanf("%d", &t);

	while (t--) {
		solve();
	}
}

int main(void) {
    // freopen(NAME".in", "r", stdin);
    // freopen(NAME".out", "w", stdout);

    #ifdef PERVEEVM_LOCAL
        auto start = std::chrono::high_resolution_clock::now();
    #endif

    run();

    #ifdef PERVEEVM_LOCAL
        auto end = std::chrono::high_resolution_clock::now();
        std::cerr << "Execution time: "
                  << std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count()
                  << " ms" << std::endl;
    #endif

    return 0;
}