#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

#define mxn 102

double a[mxn];
int n;

bool check( double d ) {
    double pre = a[1];
    for( int i = 2; i < n; ++i ) {
        if( a[i] == pre )
            continue;
        if( pre + d <= a[i] )
            pre = a[i];
        else
            if( a[i] + d > a[i+1] )
                return 0;
            else
                pre = a[i] + d;
    }
    return 1;
}
int main() {
    int cas;
    scanf( "%d", &cas );
    while( cas-- ) {
        scanf( "%d", &n );
        for( int i = 1; i <= n; ++i )
            scanf( "%lf", &a[i] );
        sort( a + 1, a + n + 1 );
        double ans = 0;
        for( int i = 1; i < n; ++i ) {
            if( check( a[i+1] - a[i] ) )
                ans = max( ans, a[i+1] - a[i] );
            if( check( ( a[i+1] - a[i] ) / 2 ) )
                ans = max( ans, ( a[i+1] - a[i] ) / 2 );
        }
        printf( "%.3lf\n", ans * 1.0 );
    }
    return 0;
}