UUIDTest.js

// based on http://stackoverflow.com/a/873856
var UUIDs = {};

var createUUID = function() {
    // http://www.ietf.org/rfc/rfc4122.txt
    var s = [];
    var hexDigits = "0123456789abcdef";
    for (var i = 0; i < 36; i++) {
        s[i] = hexDigits.substr(Math.floor(Math.random() * 0x10), 1);
    }
    s[14] = "4"; // bits 12-15 of the time_hi_and_version field to 0010
    s[19] = hexDigits.substr((s[19] & 0x3) | 0x8, 1); // bits 6-7 of the clock_seq_hi_and_reserved to 01
    s[8] = s[13] = s[18] = s[23] = "-";

    var uuid = s.join("");
    return uuid;
};

var checkUUID = function(idx) {
    if ((idx % 1000) === 0) {
        process.stdout.write(". ");
    }
    var uuid = createUUID();
    if (uuid in UUIDs) {
        console.log("UUID Collision at point", idx, uuid, "ain't unique");
        return false;
    } else {
        UUIDs[uuid] = true;
        return true;
    }
};

var runTest = function(iterations) {
    console.time('UUID Test Time');
    for (var i = 1; i <= iterations; i++) {
        if (!checkUUID(i)) {
            process.stdout.write("\n");
            console.log("Test Failed");
            console.timeEnd('UUID Test Time');
            return;
        }
    }
    process.stdout.write("\n");
    console.log("Test Completed Successfully");
    console.timeEnd('UUID Test Time');
    return;
};

module.exports = runTest(100);

Quick test create n UUID's and check for uniqueness. Used so far on 10 million generated UUID's with no duplicates found.