node.js assert module in mongodb driver documentation

Question

This is an example from mongoDB driver documentation. I've been trying to figure out what assert.equal does in the example, but the official documentation on Node.js website didn't help me too much -- The official documentation says "Tests shallow, coercive equality with the equal comparison operator ( == )." So I suspected first that it would return true or false depending on the truth value of the equality. But it seems like it doesn't.

I did look at this post: Assert module use in nodejs?. It did help -- but wasn't quite enough. I still don't really understand how "unit test" is done. Any help would be appreciated but solid examples would be super helpful!

var Db = require('mongodb').Db,
    MongoClient = require('mongodb').MongoClient,
    Server = require('mongodb').Server,
    ReplSetServers = require('mongodb').ReplSetServers,
    ObjectID = require('mongodb').ObjectID,
    Binary = require('mongodb').Binary,
    GridStore = require('mongodb').GridStore,
    Grid = require('mongodb').Grid,
    Code = require('mongodb').Code,
    BSON = require('mongodb').pure().BSON,
    assert = require('assert');

  // Set up the connection to the local db
  var mongoclient = new MongoClient(new Server("localhost", 27017), {native_parser: true});

  // Open the connection to the server
  mongoclient.open(function(err, mongoclient) {

    // Get the first db and do an update document on it
    var db = mongoclient.db("integration_tests");
    db.collection('mongoclient_test').update({a:1}, {b:1}, {upsert:true}, function(err, result) {
      assert.equal(null, err);
      assert.equal(1, result);

      // Get another db and do an update document on it
      var db2 = mongoclient.db("integration_tests2");
      db2.collection('mongoclient_test').update({a:1}, {b:1}, {upsert:true}, function(err, result) {
        assert.equal(null, err);
        assert.equal(1, result);

        // Close the connection
        mongoclient.close();
      });
    });
  });

Answer 1

Assert is used to perform a simple test to compare an expected result with an actual result. If the actual result does not match the expected result an exception will be thrown. This feature is meant for development purposes only.

It will stop the execution. I ran a simple node js server that contained an assert (assert.equal(3, 1);) and it stopped the execution because 3 does not equal 1.

The following assert will throw an exception if the parameter err is not null:

assert.equal(null, err);

See the following link for more information: https://nodejs.org/api/assert.html

Here is a description of assert from the link above:

The assert module provides a simple set of assertion tests that can be used to test invariants. The module is intended for internal use by Node.js, but can be used in application code via require('assert'). However, assert is not a testing framework, and is not intended to be used as a general purpose assertion library.