Counts documents in database

        :return: Number of documents in db

def get_documents_count(self):
        """Counts documents in database

        :return: Number of documents in db
        """
        db_collections = [
            self.database[c] for c in self.get_collection_names()
        ]  # list of all collections in database
        return sum([c.count() for c in db_collections])