Set up Tests

[Simply007]

Motivation

It would be great to have a Continuous pipeline with the tests running for all pull requests.

Proposed solution

• Choose the testing framework (we are already using Jest it is preferred one).
• Set up the test infrastructure for test
• Implement npm script called test that will run all tests
• Implement one integration test that checks the site renders three articles with specified titles

Additional context

• https://jestjs.io/docs/en/testing-frameworks#expressjs
• https://hackernoon.com/testing-node-js-in-2018-10a04dd77391
• https://medium.com/@jodylecompte/express-routes-a-tdd-approach-1e12a0799352