In software development, it is common to encounter functions or methods that interact with external services, databases, or other modules. To test these components in isolation, we can use mocks and stubs. Sinon.js is a library that facilitates the creation of mocks, stubs, and spies, and integrates seamlessly with Mocha and Chai. In this chapter, we will explain how to use Sinon.js to improve our tests.

Key Concepts

Mocks

A mock is an object that takes the place of a real object in the code and is configured to expect certain calls and behaviors. A mock can verify if a method or function has been called in the expected way.

Stubs

A stub is a function that temporarily replaces a real function and allows you to specify its behavior, such as returning a predefined value or throwing an error.

Spies

A spy is a function that records information about the interactions with other functions, such as how many times it was called or with what arguments.

Installing Sinon.js

You can install Sinon.js in your project with the following command:

shell

Using Stubs with Sinon.js

Let's say we have a function that makes a call to a database. To test this function without accessing the database, we can use a stub.

Example:

Suppose you have a function obtenerUsuarioDeDB that interacts with the database:

javascript

We want to test a function that uses obtenerUsuarioDeDB, called procesarUsuario:

javascript

Create a stub for obtenerUsuarioDeDB in a test:

javascript

Using Mocks with Sinon.js

Mocks are useful for verifying that a function is called with certain parameters. Suppose we have a function guardarUsuario that saves user data to the database.

Example:

javascript

Now we want to test another function manejarUsuario that calls guardarUsuario:

javascript

Create a mock for guardarUsuario in a test:

javascript

Using Spies with Sinon.js

Spies are useful for knowing how and when a function is called. They help to record the function interaction without changing its behavior.

Example:

javascript

Conclusion

Mocks, stubs, and spies are powerful tools for conducting more isolated and controlled tests, allowing you to simulate and verify specific code behaviors. Sinon.js provides robust functionality for working with these tools alongside Mocha and Chai, thereby improving the effectiveness and reliability of your tests. In the next chapter, we'll explore how to handle and test asynchronous functions in Node.js.