How to mock a glob call in Node.js

I'm using Mocha, Chai and Sinon JS to write Unit Tests for my Node.js application.

Here is the module I want to test:

var glob = require('glob');
var pluginInstaller = require('./pluginInstaller');

module.exports = function(app, callback) {
    'use strict';

    if (!app) {
        return callback(new Error('App is not defined'));
    }

    glob('./plugins/**/plugin.js', function(err, files) {
        if (err) {
            return callback(err);
        }

        pluginInstaller(files, callback, app);
    });
};

I have a test for the case, when there is no app using .to.throw(Error).

But I have no idea how to mock the glob call. In particular I want to tell my Test-Method, what the glob-call returns and then to check, if the pluginInstaller has been called, using sinon.spy.

Here is my test I have so far:

var expect = require('chai').expect,
pluginLoader = require('../lib/pluginLoader');

describe('loading the plugins', function() {
    'use strict';

    it ('returns an error with no app', function() {
        expect(function() {
            pluginLoader(null);
        }).to.throw(Error);
    });
});