It's probably easiest to create your query object directly as:
Test.find({
$and: [
{ $or: [{a: 1}, {b: 1}] },
{ $or: [{c: 1}, {d: 1}] }
]
}, function (err, results) {
...
}
But you can also use the Query#and helper that's available in recent 3.x Mongoose releases:
Test.find()
.and([
{ $or: [{a: 1}, {b: 1}] },
{ $or: [{c: 1}, {d: 1}] }
])
.exec(function (err, results) {
...
});