t = db.group2;
t.drop();

t.save({a: 2});
t.save({b: 5});
t.save({a: 1});

cmd = {
    key: {a: 1},
    initial: {count: 0},
    reduce: function(obj, prev) {
        prev.count++;
    }
};

result = t.group(cmd);

assert.eq(3, result.length, "A");
assert.eq(null, result[1].a, "C");
assert("a" in result[1], "D");
assert.eq(1, result[2].a, "E");

assert.eq(1, result[0].count, "F");
assert.eq(1, result[1].count, "G");
assert.eq(1, result[2].count, "H");

var keyFn = function(x) {
    return {a: 'a' in x ? x.a : null};
};

delete cmd.key;
cmd["$keyf"] = keyFn;
result2 = t.group(cmd);

assert.eq(result, result2, "check result2");

delete cmd.$keyf;
cmd["keyf"] = keyFn;
result3 = t.group(cmd);

assert.eq(result, result3, "check result3");