#include <bits/stdc++.h>
using namespace std;
 
// Speed
#define fast_io ios::sync_with_stdio(0); cin.tie(0); cout.tie(0)
 
// Typedefs
#define int long long
#define pb push_back
#define ff first
#define ss second
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) ((int)(x).size())
#define endl '\n'
#define yes cout << "YES\n"
#define no cout << "NO\n"
 
// Loops
#define rep(i,a,b) for(int i=a;i<b;++i)
#define per(i,a,b) for(int i=b-1;i>=a;--i)
#define each(x, a) for (auto& x : a)
 
// Consts
const int INF = 1e18;
const int MOD = 1e9+7;
const int N = 2e5 + 5;
 
// Math
int gcd(int a, int b) { return b == 0 ? a : gcd(b, a % b); }
int lcm(int a, int b) { return (a / gcd(a, b)) * b; }
 
int power(int a, int b, int m = MOD) {
    int res = 1;
    while (b > 0) {
        if (b & 1) res = res * a % m;
        a = a * a % m;
        b >>= 1;
    }
    return res;
}
 
int modinv(int a, int m = MOD) {
    return power(a, m - 2, m);
}
 
// Logic
void solve() {
    // Code
    int n,x;
    cin>>n>>x;
    vector<int>a(n+1);
    rep(i,0,n) cin>>a[i];
    a.push_back(x);
    sort(a.begin(),a.end());
    int d=a[0]-0;
    rep(i,1,n+1){
    	d=max(d,a[i]-a[i-1]);
    	if(a[i]==x) break;
    }
    if(x<a[n])
    cout<<d<<endl;
    else
    cout<<max(d,2*(x-a[n-1]))<<endl;
 
}
 
// Main
int32_t main() {
    fast_io;
 
    int t;
    cin >> t;
    while (t--) {
        solve();
    }
 
    return 0;
}
 

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