Differences between Chai and Sinon.js

In the world of JavaScript testing, two libraries are often used: These two are Chai and Sinon.js. In the case of any application development, both are useful tools to produce high-quality tests that can be maintained in the future. Nevertheless, they operate in different contexts in the testing system. Chai is mainly an assertion library. On the other hand, Sinon.js is a rich library of spies, mocks, and stubs.

In this article, we will discuss the difference between Chai and Sinon.js. Before discussing their differences, we must know about Chai and Sinon.js.

What is the Chai?

Chai is an assertion library that has been widely adopted in the JS ecosystem, and it is mainly used for testing. Assertions are statements that verify whether a certain expression is as expected in functional programming languages. Chai is integrated to be used with testing frameworks like mocha to allow developers to write tests with more expression. It provides three main styles of assertions.

Features of Chai:

Several features of Chai are as follows:

1. Multiple Assertion Styles:
   Chai provides three major assertion formats, namely Expect, Should, and Assert, through which developers can be flexible enough to select a specific style of their convenience.
2. Extensibility:
   Chai enables users to build his assertion functions thus making the tool very flexible and capable of being used in different testing environments and models.
3. Seamless Integration:
   Chai is easily compatible with the commonly used JavaScript testing frameworks, such as Mocha, which allows it to seamlessly blend in.
4. Rich Assertion Library:
   Chai has available assertions, such as asserting types, values, arrays, objects, functions, exceptions, and so on.

Use Cases of Chai:

Several use cases of Chai are as follows:

Validating Function Outputs:

• Utilise Chai to state that a given function holds a certain value where the argument is inserted.

Testing Object Properties:

• Check that an object possesses certain attributes and that those attributes follow the proper value range.

Verifying Array Contents:

• Chai can be used to get a pinch of confirmation, whether an array holds some elements or not or the elements are not in the correct order.

What is the Sinon.js?

Sinon.js is a library used in the development of spies, stubs, and mock, which are crucial in unit testing, particularly when there is the use of API, databases, or complex objects. Such tools assist in preventing the code under test from being influenced by other components, or in checking those interactions.

Features of Sinon.js:

Several features of Sinon.js are as follows:

1. Spies:
   Sinon.js encourages the generation of spies, which can track the arguments passed, the outcomes, values returned, and whether the function raised an exception.
2. Stubs:
   With Sinon.js, developers can write stubs by which they mimic functionalities by setting up their guidelines on how they are to operate in tests.
3. Mocks:
   Sinon.js provides mocks as a set of predefined behaviors and outcomes, which guarantee that the object interacts with its dependencies in the desired way.
4. Fakes:
   Sinon.js offers fakes, which are more simple forms of spies, stubs, and mocks, and gives a better way to construct and utilize test doubles.
5. Timers:
   Sinon.js includes features to control time in tests like fake timers, which enables developers to alter JavaScript's in-built timers (for instance setTimeout setInterval) to evaluate time-sensitive code.

Use Cases of Sinon.js:

Several use cases of Sinon.js are as follows:

Spying on Function Calls:

• Use Sinon.js spies to monitor how many times the function existed, with which parameters, and what result it produced.

Stubbing Dependencies:

• It substitutes a real function with a mock that delivers prescribed responses to see how a part of a system functions in various scenarios.

Mocking API Calls:

• It is useful to create sinon.js mocks to mimic the API calls and determine the required behavior of our application when some call comes.

Testing Time-Dependent Code:

• Use Sinon.js fake timers to choreograph when the time occurs in tests and help test functions that call on setTimeout or setInterval.

Key differences between Chai and Sinon.js

There are several key differences between Chai and Sinon.js. Some main differences are as follows: