mongodb/jstests/geo_group.js

t = db.geo_group;
t.drop();

n = 1;
for ( var x=-100; x<100; x+=2 ){
    for ( var y=-100; y<100; y+=2 ){
        t.insert( { _id : n++ , loc : [ x , y ] } )
    }
}

t.ensureIndex( { loc : "2d" } );

// Test basic count with $near
assert.eq(t.find().count(), 10000);
assert.eq(t.find( { loc : { $within : {$center : [[56,8], 10]}}}).count(), 81);
assert.eq(t.find( { loc : { $near : [56, 8, 10] } } ).count(), 81);

// Test basic group that effectively does a count
assert.eq(
  t.group( { 
    reduce : function (obj, prev) { prev.sums = { count : prev.sums.count + 1} }, 
    initial : { sums:{count:0} } } 
  ),
  [ { "sums" : { "count" : 10000 } } ]
);

// Test basic group + $near that does a count
assert.eq(
  t.group( { 
    reduce : function (obj, prev) { prev.sums = { count : prev.sums.count + 1} }, 
    initial : { sums:{count:0} },
    cond : { loc : { $near : [56, 8, 10] } } }
  ),
  [ { "sums" : { "count" : 81 } } ]
);