Unit Testing Sequelize 4 ES6 class models

In “Using ES6 classes for Sequelize 4 models” we explored how to define Sequelize models using ES6 classes.One of the benefits of such an approach is that it allows easy unit testing, it allows you to instantiate the model without the baggage of all of Sequelize (and/or a database).

The examples will use Jest module auto-mocking but should be portable to other module mocking libraries (eg. Proxyquire) with some modifications.

We’ll be testing the following model:

const { Model } = require('sequelize');

class MyModel extends Model {
  static init() {
    return super.init(
      // Config, see "Using ES6 classes for Sequelize 4 models"
    );
  }

  isAvailable (date) {
    if (!Array.isArray(this.meetings)) {
      throw new Error('meetings should be eager-loaded');
    }
    return !this.meetings.find(
      ({ startDate, endDate }) => (startDate < date && endDate > date)
    );
  }
}

module.exports = MyModel;

At the module level, we want to:

• mock out Sequelize
• import the model

In the test:

• Instantiate the model that we’ve defined (without crashing)
• Set some properties on that instance
• Run some methods
• Assert on the output

jest.mock('sequelize');
const Model = require('./model');

test('It should not throw when passed a model containing an empty list of meetings', () => {
  const model = new Model();
  model.meetings = [];
  expect(model.isAvailable.bind(null, new Date(Date.now())).not.toThrow();
});

Alternative with Object.assign

If we’re setting more than a single instance property, using Object.assign can be easier to manage:

jest.mock('sequelize');

const Model = require('./model');

test('It should not throw when passed a model containing an empty list of meetings', () => {
  const model = Object.assign(
    new Model(),
    {
      meetings: []
    }
  );
  expect(model.isAvailable.bind(null, new Date(Date.now())).not.toThrow();
});

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