mongodb/jstests/replsets/single_server_majority.js

// This test checks that w:"majority" works correctly on a lone mongod

// set up a mongod and connect a mongo
var mongod = MongoRunner.runMongod({});
var mongo = startMongoProgram("mongo", "--port", mongod.port);

// get db and collection, then preform a trivial insert 
db = mongo.getDB("test")
col = db.getCollection("single_server_majority");
col.drop();
// see if we can get a majority write on this single server
assert.writeOK(col.save({ a: "test" }, { writeConcern: { w: 'majority' }}));