#include<bits/stdc++.h>

#define int long long

#define rint register int

#define read(A) A=init()

using namespace std;

inline int init()

{

    int a=,b=;char ch=getchar();

    while(ch<''||ch>''){if(ch=='-')b=-;ch=getchar();}

    while(ch>=''&&ch<=''){a=(a<<)+(a<<)+ch-'';ch=getchar();}

    return a*b;

}

int T,n,ans;

struct node{int ds,ns,cs;}p[];

inline bool cmp(node A,node B){

    return (A.cs==B.cs)?A.ns<B.ns:A.cs<B.cs;

}

signed main()

{

//    freopen("data.in","r",stdin);

//    freopen("std.out","w",stdout);

    read(T);

    while(T--)

    {

        read(n);ans=;

        for(rint i=,ind,inn;i<=n;++i)

        {

            read(ind),read(inn);

            p[i].ds=ind,p[i].ns=inn;

            p[i].cs=inn-ind;

        }

        sort(p+,p+n+,cmp);ans=p[].ns;

        for(rint i=;i<=n;++i)ans=max(ans+p[i].ds,p[i].ns);

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

    }

}