#include <iostream>
#include <vector>
#include <climits>
using namespace std;

int main() {
	int t;
	cin >> t;
	while (t--) {
		int n, g;
		cin >> n >> g;
		vector<vector<int>> current_candidates;
		vector<int> target_bits(g);
		
		// 读取目标微缩片
		string target_str;
		cin >> target_str;
		for (int i = 0; i < g; ++i) {
			target_bits[i] = target_str[i] - '0';
		}
		current_candidates.push_back(target_bits);
		
		// 读取其他微缩片
		for (int i = 1; i < n; ++i) {
			string s;
			cin >> s;
			vector<int> bits(g);
			for (int j = 0; j < g; ++j) {
				bits[j] = s[j] - '0';
			}
			current_candidates.push_back(bits);
		}
		
		bool processed[15] = {false};
		int steps = 0;
		
		while (current_candidates.size() > 1) {
			int best_bit = -1;
			int min_count = INT_MAX;
			
			// 遍历所有未处理的位，找到最小的count
			for (int k = 0; k < g; ++k) {
				if (processed[k]) continue;
				
				int count = 0;
				for (const auto& m : current_candidates) {
					if (m[k] == target_bits[k]) {
						++count;
					}
				}
				
				// 选择最小的count，或者相同count时选最小的位
				if (count < min_count || (count == min_count && k < best_bit)) {
					min_count = count;
					best_bit = k;
				}
			}
			
			if (best_bit == -1) break; // 所有位都已处理，但理论上不可能
			
			// 过滤候选集
			vector<vector<int>> new_candidates;
			for (const auto& m : current_candidates) {
				if (m[best_bit] == target_bits[best_bit]) {
					new_candidates.push_back(m);
				}
			}
			current_candidates = move(new_candidates);
			processed[best_bit] = true;
			++steps;
		}
		
		cout << steps << endl;
	}
	return 0;
}