Mongoose validation not working properly in mocha test

I am building a REST api with nodejs, using mongoose and mochajs to run some tests. I have the following scheme:

var subscriptionTypeSchema = new mongoose.Schema({
    typeId          : { type: Number, required: true, unique: true },
    name            : { type: String, required: true},
    active          : { type: Boolean, required: true }
});

Express route:

app.post('/1.0/subscriptiontype', subscriptiontype.create);

Controller:

exports.create = function(req, res) {
    validation.subscriptionTypeValidator(req);

    var errors = req.validationErrors();
    if (errors) {
        res.status(400).json({
            errors: errors
        });
    } else {
        var subscriptionType = new SubscriptionType();
        subscriptionType.typeId = parseInt(req.body.typeId);
        subscriptionType.name = req.body.name;
        subscriptionType.active = req.body.active;
        subscriptionType.save(function(err) {
            if (err) {
                var parsedError = mongooseutility.parseMongooseError(err);
                res.status(400).json({
                    errors: [parsedError]
                });
            } else {
                res.json({identifier: subscriptionType._id});
            }
        });
    }
};

The mongoose utility maps the error codes to a more API friendly output (error codes 11001 and 11000 are mapped to a 'duplicate' error, as can be seen in the test).

Mocha before method:

before(function(done) {
    db.connection.on('open', function() {
        db.connection.db.dropDatabase(function(err) {
            done();
        });
    });
});

I've verified that the database is dropped successfully.

The test itself makes a request using supertest. Before this test, I have a test that creates a subscription type with typeId 4 successfully, so this one should fail:

it('Should not create subscription with taken type id', function (done) {
    request(app.privateapi)
        .post('/1.0/subscriptiontype')
        .set('Authorization', authorizationHeader)
        .send({
            typeId: 4,
            name: 'New package',
            active: 1
        })
        .expect(function (res) {
            if (res.status !== 400) {
                throw new Error('Status code was not 400');
            }

            var expectedResponse = { errors: [ { param: 'typeId', msg: 'duplicate' } ] };

            if (JSON.stringify(res.body) !==  JSON.stringify(expectedResponse)) {
                throw new Error('Output was not was as expected');
            }
        })
       .end(done);
});

Tests are invoked using grunt-simple-mocha.

This test works the first time, however when I run it a 2nd time it fails on the unique validation. A third time it works again. I've done some searching and found that it probably has something to do with a race condition while recreating indexes, so I've tried restarting mongodb before running the tests again, but that doesn't work. I've found a solution here: http://ift.tt/1G5ToGR but I am not sure how to implement this. Any ideas?

Edit: for now I fixed it by dropping the database in an 'after' method (instead of 'before'). All the tests run fine, but it would be nice to keep the test data after the tests are done, for inspection etc...