内容简介:Like the name says, it’s basically a snapshot of output, you want to compare over time and test if the code is up to the expectations. For example, let’s say you have written a React component which renders some UI. Over the time, different people work on
Jest is a JavaScript testing framework built by Facebook . It has the test runner, test evaluator and assertions utilities built in. It’s an amazing framework to use for testing your applications, may it be written in React , Angular or Vue . In this article, I will explain what is Snapshot feature of Jest and show an interesting use case which can make your testing simpler and faster.
What is Snapshot?
Like the name says, it’s basically a snapshot of output, you want to compare over time and test if the code is up to the expectations. For example, let’s say you have written a React component which renders some UI. Over the time, different people work on it and change the UI output of it. This is stored as a text as shown below and a simple diff comparison of the text outputs can tell if the code is giving the correct output. The main interest of this feature is to make testing easier and painless, testing the goals of your App to render certain UI and not to worry about the implementations.
Though this snapshotting is widely used for testing React components, you can use to test the any output that can be serializable , for example objects or json.
The Case
Lets say, you have a configuration file exporting different values as one below:
// config.js export const APP_NAME = 'MY_APP'; export const APP_MAIN_ROUTE = 'app/main'; export const APP_USER_ROUTE = 'app/user';
Ealier, I used to write a test, which used to import all these params and do individual assertions, or write some wrapper logic to get it working with a single assertion. But with Jest snapshot, it’s way simplified, as one below:
// config.test.js
import * as constants from '<source-file-path>';
test('constants matches snapshot', () => {
expect(constants).toMatchSnapshot();
});
On the first run, it will create a snapshot file, as shown below and compare against it on future runs.
// config.test.js.snap
// Jest Snapshot v1, https://goo.gl/fbAQLP
exports[`constants matches snapshot 1`] = `
Object {
"APP_NAME": "MY_APP",
"APP_MAIN_ROUTE": "app/main",
"APP_USER_ROUTE": "app/user",
}
`;
If you have a very huge, nested object (probably a configuration object), you can test it via snapshotting with a single line . A lot of assertion or implementation related coding can be avoided. Make sure to give this a try and let me know your thoughts in comments.
Thanks a lot for reading through. Please let me know how you felt and if you would like to hear more on any topic, don’t forget to let me know in comments. Have a good day!
以上就是本文的全部内容,希望本文的内容对大家的学习或者工作能带来一定的帮助,也希望大家多多支持 码农网
猜你喜欢:本站部分资源来源于网络,本站转载出于传递更多信息之目的,版权归原作者或者来源机构所有,如转载稿涉及版权问题,请联系我们。
现代操作系统(原书第4版)
[荷] Andrew S. Tanenbaum、[荷] Herbert Bos / 陈向群、马洪兵 等 / 机械工业出版社 / 2017-7 / 89.00
Andrew S. Tanenbaum教授编写的教材《现代操作系统》现在已经是第4版了。第4版在保持原有特色的基础上,又增添了许多新的内容,反映了当代操作系统的发展与动向,并不断地与时俱进。 对比第3版,第4版有很多变化。一些是教材中多处可见的细微变化,一些是就某一功能或机制增加了对最新技术的介绍,如增加了futex同步原语、读–复制–更新(Read-Copy-Update)机制以及6级RA......一起来看看 《现代操作系统(原书第4版)》 这本书的介绍吧!