Java: Mongo fails to assert the right number of documents inserted

Question

I have a following test

    @Test
    public void testPutDocuments() throws Exception {
        final DBObject document01 = new DBObject();
        document01.put("uniqueId", "001");
        document01.put("rv", "values");
        document01.put("pv", "values");

        final DBObject document02 = new DBObject();
        document02.put("uniqueId", "002");
        document02.put("rv", "values");
        document02.put("pv", "values");

        final DBObject document03 = new DBObject();
        document03.put("uniqueId", "003");
        document03.put("rv", "values");
        document03.put("pv", "values");

        final List<DBObject> documents = new ArrayList<DBObject>();
        documents.add(document01);
        documents.add(document02);
        documents.add(document03);

        mongoRule.getMongoService().putDocuments(documents);
        assertEquals(3, mongoRule.getDatabase().getCollection("test").getCount());
    }

Where mongoRule is a rule which connects to database, provides MongoService(a wrapper written to mongo client)

MongoService related methods

public void putDocument(@Nonnull final DBObject document) {
    LOGGER.info("inserting document - " + document.get("uniqueId"));
    mongo.getDB(database).getCollectionFromFull(getCollectionName(document)).insert(document);
}

public void putDocuments(@Nonnull final List<DBObject> documents) {
    for (final DBObject document : documents) {
        putDocument(document);
    }
}

When I run this, I get

java.lang.AssertionError: 
Expected :3
Actual   :1  

Now, if I do this

  mongoRule.getMongoService().putDocuments(documents);
  Thread.sleep(1000); 
  assertEquals(3, mongoRule.getDatabase().getCollection("contract").getCount());

I see no error.

Question:
a.) Why sleeping a thread for a second helped in getting a right number. isn't it a concurrency related issue? What if two threads are trying to put same documents where as document has to be unique.
b.) How can I fix this?

Thank you

Answer 1

answered here - https://groups.google.com/forum/?fromgroups#!topic/mongodb-user/jyvMkDFVous