Using Frisby.js to test your API

Why test your API?

Testing an API is important because it allows you to assert that you are conforming to the interface in which you promise to deliver. Testing a the API layer explicitly allows you to catch code changes that change data types, number of return values, etc… and can be an important trigger for you to update your unit tests and API Docs.

Why can’t I just unit test?

Unit testing is intended for the developer to vet the units of their code. You should worry about testing at the *method* level and not necessarily how it all fits together. By introducing API testing, you’ll be able to get a better handle on whether you’re using appropriate mock data in your tests and asserting the correct return values.

Well can’t I just rely on automated testing instead?

Automation suites, such as Selenium do not test at the API level; rather, they test at the user interface level. Sure, you could build your own automated tool to explicitly use your API to test behavior, but again, you are not testing the purity and correctness of the API. Sure, if your test uses the API a certain way and a developer breaks it, you can detect API failures. However, these types of tests don’t necessarily check for parameter correctness and all variations of use of an API.

API Testing Example

This is where Frisby.js comes into play. Frisby.js is a JavaScript-based API testing framework that makes it incredibly simple for you to test against your API. Here is an example:

Getting set up

Install Frisby.js + Jasmine Node

Test Structure

Frisby tests require that you reference the frisby global variable. From here, you can call frisby.create to create the structure of your first test:

Write your first test

Let’s say your website allows you to check a stock price by passing in a stock symbol. This is a GET request and takes one required parameter, symbol,  and one optional parameter, timestamp. If timestamp is passed in, the API will retrieve the stock price, if available, at the given timestamp. Otherwise, it will return the latest stock price.

In this example, we used Frisby.js to assert the validity of the response both in TYPES and in values, once we could narrow the stock down to a particular time. In one short test, we tested the response code, the header contents, and the JSON body of the response. Be sure to check out the Frisby.js API for detailed descriptions on each of the statements above.

In conclusion…

In this blog post, we explored WHY we test an API vs. unit testing vs. automated testing and went through a simple example on how to write a test against a simple API. API testing is important because it will help you identify breaking API changes from code that may otherwise been unnoticed. Also, it helps you keep your mock data/unit tests up to date and identify changes needed in your API documentation.

In a future blog post, I will dive deeper into Frisby.js and show you how you can write tests that depend on one another (think OAuth tokens and needing a token for a subsequent test) as well as a few more advanced examples.