//A tree without skin will surely die.
//A man without face will be alive.
#include<bits/stdc++.h>
using namespace std;
#define mid ((l+r)>>1)
#define rep(i,j,k) for (int i=j;i<=k;++i)
#define per(i,j,k) for (int i=j;i>=k;--i)
int const N=1e5+10;
struct frac{int x,y;};
int n,L,ax,ay,lf[20],pre[20][N],nxt[20][N],len[20][N],sm[N];
string s[20];
inline bool dfs(int S,int sz){
	if (S==(1<<n)-1) return 1;
	pair<int,int>a1={1e9,-1},a2={1e9,-1};
	rep(i,0,n-1){
		if (S>>i&1) continue;
		int pos=lf[sz];
		rep(i,1,sz){
			int r=lf[i]+ax;
			if (r>pos) pos=max(pos,min(r,pre[sz-i+1][(r+ay-1)/ay]*ay));
		}
		if (len[i][pos/ay]*ay-(pos%ay)<ax){
			pos=nxt[i][(pos+ay-1)/ay];
			if (pos==-1) continue;
			pos*=ay;
		}
		if (pos<a1.first) a1={pos,i};
		else if (pos<a2.first) a2={pos,i};
	}
	if (a1.second!=-1){
		lf[sz+1]=a1.first;
		if (dfs(S|(1<<a1.second),sz+1)) return 1;
	}
	if (a2.second!=-1){
		lf[sz+1]=a2.first;
		if (dfs(S|(1<<a2.second),sz+1)) return 1;
	}
	return 0;
}
inline bool check(int a,int b){
	ax=a,ay=b;
	memset(pre,0,sizeof(pre));
	memset(nxt,0,sizeof(nxt));
	memset(len,0,sizeof(len));
	rep(i,0,n-1){
		per(j,L-1,0) len[i][j]=(s[i][j]=='.' && sm[j]>1)?len[i][j+1]+1:0;
		nxt[i][L]=-1;
		per(j,L-1,0) nxt[i][j]=len[i][j]*ay>=ax?j:nxt[i][j+1];
	}
	rep(i,0,n-1) rep(j,1,L){
		pre[i][j]=sm[j-1]==i+1?j:pre[i][j-1];
		if (i) pre[i][j]=max(pre[i][j],pre[i-1][j]);
	}
	return dfs(0,0);
}
inline void solve(){
	cin>>n>>L;
	rep(i,0,n-1) cin>>s[i];
	rep(i,0,L-1){
		sm[i]=0;
		rep(j,0,n-1) sm[i]+=s[j][i]=='.';
		if (!sm[i]) return cout<<"-1\n",void();
	}
	vector<frac>fracs;
	rep(i,0,L) rep(j,1,n)
		if (__gcd(i,j)==1) fracs.push_back((frac){i,j});
	sort(fracs.begin(),fracs.end(),[](frac &x,frac &y){
		return x.x*y.y<y.x*x.y;
	});
	int l=1,r=(int)fracs.size()-1,ans=0;
	while (l<=r)
		if (check(fracs[mid].x,fracs[mid].y)) l=(ans=mid)+1;
		else r=mid-1;
	cout<<fracs[ans].x<<'/'<<fracs[ans].y<<'\n';
}
signed main(){
	ios::sync_with_stdio(false);
	cin.tie(0),cout.tie(0);
	int t=1;
	cin>>t;
	while (t--) solve();
	return 0;
}