#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
#include<vector>
#include<cmath>
using namespace std;

char B[505][505];
bool adj[505][505];
bool visit[505][505];
int w,h;
int cycle;

int getMax2s(int y, int x) {
    if(visit[y][x] || y < 0 || y >= h || x < 0 || x >= w) return 0;
    visit[y][x] = 1;
    int cnt = 1;
    int child = 0;
    if (y-1 >= 0 && adj[y-1][x]) {
        child++;
        cnt += getMax2s(y-1, x);
    }
    if (y+1 < h && adj[y+1][x]) {
        child++;
        cnt += getMax2s(y+1, x);
    }
    if (x-1 >= 0 && adj[y][x-1]) {
        child++;
        cnt += getMax2s(y, x-1);
    }
    if (x+1 < w && adj[y][x+1]) {
        child++;
        cnt += getMax2s(y, x+1);
    }
    cycle = min(cycle, child);
    return cnt;
}

int main() {
    int cases;
    scanf("%d", &cases);
    while(cases--) {
        scanf("%d %d", &w, &h);
        for (int i = 0; i < h; i++) {
            scanf("%s", B[i]);
        }
        memset(adj, 0, sizeof(adj));
        memset(visit, 0, sizeof(visit));
        for (int i = 0; i < h; i++) {
            for (int j = 0; j < w; j++) {
                int cnt = 0;
                if (B[i][j] == '.') continue;
                if (i-1 >= 0 && B[i-1][j] == '*') cnt++;
                if (i+1 < h && B[i+1][j] == '*') cnt++;
                if (j-1 >= 0 && B[i][j-1] == '*') cnt++;
                if (j+1 < w && B[i][j+1] == '*') cnt++;
                if (cnt == 2) {
                    adj[i][j] = 1;
                }
            }
        }
        int maxv = 0;
        cycle = 1000;
        for (int i = 0; i < h && cycle != 2; i++) {
            for (int j = 0; j < w; j++) {
                if (!adj[i][j] || visit[i][j]) continue;
                cycle = 1000;
                int res = getMax2s(i, j);
                if (cycle == 2) break;
                maxv = max(maxv, res);
            }
        }
        if (cycle == 2) printf("-1\n");
        else printf("%d\n", (maxv+1)/2+1);
    }
}