@space-labs/osnap v1.5.3

OSnap

:warning: This library is currently in an alpha phase. There may be breaking changes and unexpected errors! :warning:

OSnap is a snapshot testing tool, which uses Chrome to take screenshots and compares them with a base image taken previously.

If both images are equal, the test passes. If the images aren't equal, the test fails and OSnap puts the new image into a new "__updated__" folder inside of your snapshot folder. It also generates a new image inside of a "__diff__" folder, which shows the base image (how it looked before), an image with the differing pixels highlighted and the new image side by side.

OSnap mainly focuses on speed and ease of use. A Project with around 1200 snapshots will run in under 2 minutes*, compared to around 18 minutes it takes other popular snapshot tools to run the same test suite.

* with 20 parallel runners on a 2017 15-inch MacBook Pro.

Table of contents

• How do I install it?
• How do I use it?
  • Global Config
  • Test Config
  • Using Actions
  • CLI Flags
  • Updating Snapshots
• Credits
• Todos

How do I install it?

OSnap may be installed with yarn or npm using one of the following commands:

yarn add @space-labs/osnap --dev

or

npm install @space-labs/osnap --save-dev

How do I use it?

Before you can run your first test suite, OSnap needs to be configured. To do this, you need at least two files. The global config file and at least one test file.

After you have created them as explained below, you just have to run yarn osnap, npx osnap or create a npm script running osnap with the optional cli flags available.

Global Config

The global config file has to be named osnap.config.json and lives in the root folder of your project (where your package.json is located). If you want to have the config file in a different location, you may specify the --config option as a cli option.

The following options are available:

Keys marked with * are required!

Full example of a osnap.config.json:

{
  "baseUrl": "http://localhost:3000",
  "fullScreen": true,
  "threshold": 3,
  "parallelism": 20,
  "testPattern": "src/**/*.osnap.json",
  "ignorePatterns": ["node_modules", "vendor", "dist"],
  "defaultSizes": [
    { "width": 1600, "height": 900 },
    { "width": 1366, "height": 768 },
    { "width": 1024, "height": 576 },
    { "width": 768, "height": 432 },
    { "width": 640, "height": 360 },
    { "width": 320, "height": 180 }
  ],
  "snapshotDirectory": "./__image-snapshots__",
  "diffPixelColor": {
    "r": 0,
    "g": 255,
    "b": 0
  }
}

Test Config

The test config files (**.osnap.json by default), are used to specify a single test to be executed on all defaultSizes. A test file consists of an array of tests with the following possible options:

Keys marked with * are required!

The smallest possible test file would look like this:

[
  {
    "name": "Login",
    "url": "/path/to/login.html"
  }
]

Full example of a test file:

[
  {
    "name": "Home",
    "url": "/",
    "threshold": 20,
    "sizes": [{ "width": 768, "height": 1024 }],
    "actions": [
      { "action": "type", "selector": "#search", "text": "some text to type" },
      { "action": "click", "selector": "#id .class" },
      { "action": "wait", "timeout": 2000 }
    ]
  }
]

Using Actions

As seen in the full example above, you are able to run some actions, before the screenshot will be taken. This is useful to bring the page into a specific state, you want to capture. For example: opening a dropdown, typing something in an input or waiting for an animation to be completed.

The currently available actions are wait, click and type. They may be configured like this:

Wait:

{ "action": "wait", "timeout": 2000 }

Click:

{ "action": "click", "selector": "#id-to-click" }

Type:

{ "action": "type", "selector": "#search", "text": "some searchword" }

CLI Flags

The following cli flags are currently available and should be used mainly in ci environments.

Updating Snapshots

There is no "update" command to update the snapshots. If the changes shown in the diff image are expected, you just have to move and replace the image from the "__updated__" folder into the "__base_images__" folder.

Credits

ODiff: ODiff inspired the name of this library and is used as the underlying diffing algorithm. Thank you for your work @dmtrKovalenko!

Some things we still want to add:

In decending order of priority (top ones are more important):

• Official Docker base image: Snapshot tests are by nature pretty susceptible to the smallest changes in rendering. A huge problem is, that Browsers render (mainly fonts and images) different on different devices and operating systems. For the human eye, this is mostly not noticeable, but for an diffing algorithm, these changes are noticeable and will fail the test. So it is important to always run the tests in the same environment.
• Ignore Regions: Ignore regions of the snapshot, you know will always be different.
• Listen for network requests: Wait for specific network requests to finish, before taking the screenshot. For example: Wait for a failed login attempt to come back, to screenshot the error state
• Wait for dom events: Maybe we can find a way, to wait for specific events to be triggered on the page. For example: Wait for all animations on the page to complete before taking the screenshot.

If you find a bug or think some feature is missing, don't hesitate to file an issue.