#include <bits/stdc++.h>
#define int ll
#define mkp make_pair
#define fi first
#define se second
#define debug(x) cerr<<"line: "<<__LINE__<<" with "<<x<<"\n"
using namespace std;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int,int>;
using vi = vector<int>;
const int mod = 998244353;
template<class T>bool chkMin(T &x,T y){if(x>y)return x=y,true;return false;}
template<class T>bool chkMax(T &x,T y){if(x<y)return x=y,true;return false;}
template<class T>void moder(T &x){x%=mod;}
const int MAXN = 300005;
int n,k;
ll a[MAXN],cf[MAXN];
ll pre[MAXN],suf[MAXN];
bool valid(int x){return 1<=x&&x<=n;}
ll seg[MAXN<<2];
#define ls (p<<1)
#define rs (p<<1|1)
void build(int lp,int rp,int p){
	if(lp==rp){
		seg[p]=abs(cf[lp]);return;
	}int mid = (lp+rp)/2;
	build(lp,mid,ls);build(mid+1,rp,rs);
	seg[p]=__gcd(seg[ls],seg[rs]);
}
ll query(int l,int r,int lp=1,int rp=n,int p=1){
	if(l<=lp && r>=rp)return seg[p];
	int mid = (lp+rp)/2;
	if(l<=mid && r>mid)return __gcd(query(l,r,lp,mid,ls),
									query(l,r,mid+1,rp,rs));
	if(l<=mid)return query(l,r,lp,mid,ls);
	if(r>mid)return query(l,r,mid+1,rp,rs);
	assert(0);
	return 666;
}
void solve(){
	cin>>n>>k;
	for(int i=1;i<=n;i++)cin>>a[i];
	for(int i=1;i<=n;i++)cf[i]=a[i]-a[i-1];
	pre[1]=cf[1], suf[n]=abs(cf[n]);
	for(int i=2;i<=n;i++)pre[i]=__gcd(pre[i-1],abs(cf[i]));
	for(int i=n-1;i>=1;i--)suf[i]=__gcd(suf[i+1],abs(cf[i]));
	vector<int> L,R;
	pre[0]=suf[n+1]= -1;
	build(1,n,1);
	for(int i=0;i<=n;i++){
		if(pre[i]!=pre[i+1])L.push_back(i+1),L.push_back(i);
	}
	for(int i=n+1;i>=1;i--){
		if(suf[i]!=suf[i-1])R.push_back(i-1),R.push_back(i);
	}
	ll ans = pre[n]; 	
	for(int i=1;i<=n;i++){
		ll res = abs(cf[i]+k);
		if(i>1)res=__gcd(res,pre[i-1]);
		if(i<n)res=__gcd(res,suf[i+1]);
		ans=max(ans,res);
	}
	
	for(int i=1;i<n;i++){
		ll res = __gcd(abs(cf[i]+k),abs(cf[i+1]-k));
		if(i>1)res=__gcd(res,pre[i-1]);
		if(i+1<n)res=__gcd(res,suf[i+2]);
		ans=max(ans,res);
	}
	
	for(int i : L){
		if(!valid(i))continue;
		for(int j : R){
			if(i>=j || !valid(j)){continue;}
			ll res = __gcd(abs(cf[i]+k),abs(cf[j]-k));
			if(i>1)res=__gcd(res,pre[i-1]);
			if(j<n)res=__gcd(res,suf[j+1]);
			if(i+1<=j-1)res=__gcd(res,query(i+1,j-1));
			ans=max(ans,res);
			//cerr<<"With L="<<i<<", R="<<j-1<<" get"<<res<<"\n";
		}
	}
	cout<<ans<<"\n";
}
signed main() {
	//cerr<<(&s1-&s2)/1024.0/1024<<" ";
	cin.tie(nullptr)->sync_with_stdio(false);
	int T;cin>>T;
	while(T--)solve();
	return 0;
}