const maxn=;

var

 h,sum,rank,x,y,sa,c,lx,rx,col:array[..maxn] of longint;

 n,k,maxlen,t,q:longint;

 s:ansistring;

function max(x,y:longint):longint; begin if x>y then exit(x) else exit(y); end;

function min(x,y:longint):longint; begin if x<y then exit(x) else exit(y); end;

procedure swap(var x,y:longint); var tmp:longint; begin tmp:=x;x:=y;y:=tmp; end;

procedure make;

var p,i,j,tot:longint;

begin

 while p<n do

  begin

   fillchar(c,sizeof(c),);

   for i:=  to n-p do y[i]:=rank[i+p];

   for i:= n-p+ to n do y[i]:=;

   for i:=  to n do inc(c[y[i]]);

   for i:=  to n do inc(c[i],c[i-]);

   for i:=  to n do

    begin

     sa[c[y[i]]]:=i;

     dec(c[y[i]]);

    end;

   fillchar(c,sizeof(c),);

   for i:=  to n do x[i]:=rank[i];

   for i:=  to n do inc(c[x[i]]);

   for i:=  to n do inc(c[i],c[i-]);

   for i:= n downto  do

    begin

     y[sa[i]]:=c[x[sa[i]]];

     dec(c[x[sa[i]]]);

    end;

   for i:=  to n do sa[y[i]]:=i;

   tot:=;

   rank[sa[]]:=;

   for i:=  to n do

    begin

     if (x[sa[i]]<>x[sa[i-]]) or (x[sa[i]+p]<>x[sa[i-]+p]) then inc(tot);

     rank[sa[i]]:=tot;

    end;

   if tot=n then break;

   p:=p<<;

  end;

 for i:=  to n do sa[rank[i]]:=i;

 h[]:=; p:=;

 for i:=  to n do

  begin

   p:=max(p-,);

   if rank[i]= then continue;

   j:=sa[rank[i]-];

   while (j+p<=n) and (i+p<=n) and (s[i+p]=s[j+p]) do inc(p);

   h[rank[i]]:=p;

  end;

end;

procedure init;

var i,j,tot,p,m:longint;

 s1:ansistring;

begin

 readln(k);

 readln(s);

 for i:=  to length(s) do col[i]:=;

 maxlen:=length(s);

 for i:=  to k do

  begin

   readln(s1);

   maxlen:=max(length(s1),maxlen);

   s:=s+'#';

   for j:= length(s)+ to length(s)+length(s1) do col[j]:=i;

   s:=s+s1;

  end;

 n:=length(s);

 fillchar(c,sizeof(c),);

 for i:=  to n do x[i]:=ord(s[i]);

 for i:=  to n do inc(c[x[i]]);

 for i:=  to  do inc(c[i],c[i-]);

 for i:=  to n do

  begin

   sa[c[x[i]]]:=i;

   dec(c[x[i]]);

  end;

 tot:=;

 rank[sa[]]:=;

 for i:=  to n do

  begin

   if x[sa[i]]<>x[sa[i-]] then inc(tot);

   rank[sa[i]]:=tot;

  end;

 make;

end;

function check(len:longint):boolean;

var i,j,t,cnt:longint;

begin

 for i:=  to n do

  begin

   if h[i]<len then

    begin

     fillchar(lx,sizeof(lx),$7f);

     fillchar(rx,sizeof(rx),);

     lx[col[sa[i]]]:=sa[i];

     rx[col[sa[i]]]:=sa[i];

    end

   else

    begin

     t:=col[sa[i]];

     lx[t]:=min(lx[t],sa[i]);

     rx[t]:=max(rx[t],sa[i]);

     cnt:=;

     for j:=  to k do if rx[j]-lx[j]+>=len then inc(cnt);

     if cnt=k then exit(true);

    end;

  end;

 exit(false);

end;

procedure solve;

var l,r,mid,ans:longint;

begin

 l:=; r:=maxlen; ans:=;

 while l<=r do

  begin

   mid:=(l+r)>>;

   if check(mid) then

    begin

     ans:=mid;

     l:=mid+;

    end

   else r:=mid-;

  end;

 writeln(ans);

end;

Begin

 readln(t);

 for q:=  to t do

  begin

   init;

   solve;

  end;

End.