Unit Test Functions Connecting to a Postgres DB

Question

I am using mocha, nodejs and pg-promise connecting to a Postgres db. I am wondering how can I unit test a function that executes a DML? This is just a simple example:

export function insertUser(db, { firstName, lastName }) {
  db.one(`
    INSERT INTO users
    (
      firstName,
      lastName
    )
    VALUES
    (
      $<firstName>,
      $<lastName>
    )
  `, { firstName, lastName });
}

If there is a typo in the query, how can the unit test capture it? I can create a test db, creating temporary tables on the fly but this will cause my test to slow down.

Answer 1

Given that the db variable is a function parameter, unit-testing this type of code will be straight-forward.

Go ahead and install a mocking library. We have had good success with sinonjs.

npm install sinon --save-dev

With the mock library in place you can now create the unit-test, something along the lines as follows:

const should = require('should'),
      sinon = require('sinon'),
      helper = require('your-db-module');

describe('DB functions', () => {
  describe('insertUser', () => {
    const { insertUser } = helper;

    it('correctly inserts a new user', () => {
      const db = {
        one: sinon.stub()
      };

      insertUser(db, { firstName: 'john', lastName: 'doe' });

      db.one.calledWithExactly('INSERT INTO users(firstName, lastName) VALUES($<firstName>, $<lastName>)', { firstName: 'john', lastName: 'doe'}).should.eql(true);
    });
  });
});

That should set you off on the right foot.