import java.util.*; 
import java.io.*;
import java.math.*;
import java.util.stream.*;
import java.util.function.*;

class Main implements Runnable {

    public void solve() {    
        int t = in.nextInt() ;
        while(t-->0) {
            int n = in.nextInt();
            long [] a = in.nextLong(n);
            long l = -1 , r = (long) 1e9;
            while(r - l > 1) {
                long mid = (l + r) / 2 ;
                boolean inc = true ;
                for(int i = 0 ; i < n - 1; i ++) {
                    if((a[i] + ((mid) * (i + 1))) >= (a[i + 1] + ((mid) * (i + 2)))) inc = false ;
                }
                if(inc) r = mid ;
                else l = mid ;
            }
            out.println(r);
        }
    }

    /******/



    /******/
    
    public PrintWriter out = new PrintWriter(System.out);
    public In in = new In() ;
    public static final int  inf = (1  << 30);
    public static final long lnf = (1L << 60);
    public static final String yes = "Yes" , no  = "No" ;
    public static final int mod7 = 1000000007 , mod9 = 998244353;
    public static final int [] dy4 = {-1,0,1,0} , dx4 = {0,1,0,-1};
    public static final int [] dy8 = {-1,-1,-1,0,1,1,1,0} , dx8 = {-1,0,1,1,1,0,-1,-1};

    public static void main(String ... args) { new Thread(null, new Main(), "", Runtime.getRuntime().maxMemory()).start(); }
    public void run() { solve(); out.flush(); }

}

class In {

    private final InputStream in = System.in;
    private final Scanner sc = new Scanner(System.in);
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;

    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }

    private int readByte() { 
        if (hasNextByte()) return buffer[ptr++]; else return -1;
    }

    private static boolean isPrintableChar(int c) { 
        return 33 <= c && c <= 126;
    }

    private  boolean hasNext() { 
        while(hasNextByte() && !isPrintableChar(buffer[ptr])) {
            ptr++; 
        }
        return hasNextByte();
    }
    
    public String next() {
        if (!hasNext()) throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while(isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }

    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
        return (int) nl;
    }

    public double nextDouble() { 
        return Double.parseDouble(next());
    }

    public char nextChar() {
        return next().charAt(0);
    }

    public BigInteger nextBigInteger() {
        return sc.nextBigInteger();
    }

    public int [] nextInt(int n) {
        int [] array = new int[n];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = nextInt();
        }
        return array ;
    }

    public int [][] nextInt(int n , int m) {
        int [][] array = new int[n][m];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = nextInt(m);
        }
        return array ;
    }

    public long [] nextLong(int n) {
        long [] array = new long[n];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = nextLong();
        }
        return array ;
    }

    public long [][] nextLong(int n , int m) {
        long [][] array = new long[n][m];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = nextLong(m);
        }
        return array ;
    }

    public double [] nextDouble(int n) {
        double [] array = new double[n];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = nextDouble();
        }
        return array ;
    }
    
    public String [] next(int n) {
        String [] array = new String[n];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = next();
        }
        return array ;
    }

    public String [][] next(int n , int m) {
        String [][] array = new String[n][m];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = next(m);
        }
        return array ;
    }

    public char [] nextChar(int n) {
        char [] array = new char[n];
        String string = next() ;
        for(int i = 0 ; i < n ; i ++) {
            array[i] = string.charAt(i);
        }
        return array ;
    }

    public char [][] nextChar(int n , int m) {
        char [][] array = new char[n][m];
        for(int i = 0 ; i < n ; i ++) {
            array[i] = nextChar(m);
        }
        return array ;
    }

}