db.jstests_capped.drop();
db.createCollection("jstests_capped", {capped:true, size:30000});
assert.eq( 0, db.system.indexes.find( {ns:"test.jstests_capped"} ).count() );
t = db.jstests_capped;

t.save({x:1});
t.save({x:2});

assert( t.find().sort({$natural:1})[0].x == 1 );
assert( t.find().sort({$natural:-1})[0].x == 2 );