mongo/jstests/replsets/single_server_majority.js

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

// set up a mongod and connect
var mongod = MongoRunner.runMongod({});

// get db and collection, then perform a trivial insert
db = mongod.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' }}));