#include <iostream>
#include <cstdint>
#include <vector>

using namespace std;

int main()
{
	cin.tie(nullptr);
	ios::sync_with_stdio(false);

	int32_t T, i, j;
	cin >> T;
	vector<int32_t> N(T);
	vector<vector<int32_t>> A(T, vector<int32_t>());
	for (i = 0; i != T; ++i)
	{
		cin >> N[i];
		A[i].resize(N[i]);
		for (j = 0; j != N[i]; ++j)
			cin >> A[i][j];
	}

	for (i = 0; i != T; ++i)
	{
		auto l = -1, r = 1'000'000'001;
		while (l + 1 < r)
		{
			const auto c = (l + r) / 2;
			for (j = 1; j != N[i]; ++j)
				if (A[i][j - 1] + static_cast<int64_t>(j) * c >= A[i][j] + static_cast<int64_t>(j + 1) * c)
					break;

			if (j == N[i]) r = c;
			else l = c;
		}

		cout << r << '\n';
	}

	return 0;
}