Node mongodb driver can insert, count, but find - node.js

Question

I am migrating an existing app to mongodb,
I have this code mostly found on the node native mongodb driver site.
var fs = require('fs-extra');
var MongoClient = require('mongodb').MongoClient;
const mongoConfig = JSON.parse(fs.readFileSync("./configuration/mongo.json", "utf-8").toString());
const assert = require('assert');
const insertDocuments = function(db, callback) {
// Get the documents collection
const collection = db.collection('documents');
// Insert some documents
collection.insertMany([
{a : 1}, {a : 2}, {a : 3}
], function(err, result) {
assert.equal(err, null);
assert.equal(3, result.result.n);
assert.equal(3, result.ops.length);
console.log("Inserted 3 documents into the collection");
callback(result);
});
};
const findDocuments = function(db, callback) {
// Get the documents collection
const collection = db.collection('documents');
// Find some documents
collection.find({}).toArray(function(err, docs) {
assert.equal(err, null);
console.log("Found the following records");
console.log(docs)
callback(docs);
});
};
function initDb() {
var uri = "mongodb://" + mongoConfig.user + ":" + mongoConfig.pass + "#" + mongoConfig.host + ":" + mongoConfig.port;
MongoClient.connect(uri, {auth: {user: mongoConfig.user, password: mongoConfig.pass}, authSource: mongoConfig.dbname}, function (err, client) {
if (err) {
console.error(err);
}
const db = client.db('test');
insertDocuments(db, function() {
findDocuments(db, function() {
client.close();
});
});
}
initDb();
Then i get the following output in the console :
Inserted 3 documents into the collection
Found the following records
[]
Using Robomongo from the same computer to the same server using same credentials, i am able to see and edit the datas.
the insert is working fine, as i am writing this i have a dozen of test documents inserted this way.
But find allways return an empty array.
However, using count instaed of toArray returns the corret value.
I am using :
"mongodb": "^3.0.5",
From my package.json
What am i missing pls ?