Storybook Addon Coverage

Tools to support code coverage in Storybook and the Storybook test runner. It supports Storybook projects that use Webpack5 or Vite.

Installation

Install this addon by adding the @storybook/addon-coverage dependency:

yarn add -D @storybook/addon-coverage

And by registering it in your .storybook/main.js:

export default {
  addons: ["@storybook/addon-coverage"],
};

Configuring the addon

This addon instruments your code by using a custom wrapper around istanbul-lib-instrument if your project uses Webpack5 or vite-plugin-istanbul if your project uses Vite. It provides some default configuration, but if you want to add yours, you can do so by setting the options in your .storybook/main.js:

export default {
  addons: [
    {
      name: "@storybook/addon-coverage",
      options: {
        istanbul: {
          include: ["**/stories/**"],
        },
      },
    },
  ],
};

The available options if your project uses Webpack5 are as follows:

Option name	Description	Type	Default
cwd	Set the working directory	String	process.cwd()
nycrcPath	Path to specific nyc config to use instead of automatically searching for a nycconfig.	string	-
include	Glob pattern to include files. It has precedence over the include definition from your nyc config	Array<String>	-
exclude	Glob pattern to exclude files. It has precedence over the exclude definition from your nyc config	Array<String>	defaultExclude in https://github.com/storybookjs/addon-coverage/blob/main/src/constants.ts
extension	List of supported extensions. It has precedence over the extension definition from your nyc config	Array<String>	['.js', '.cjs', '.mjs', '.ts', '.tsx', '.jsx', '.vue', '.svelte]
coverageVariable	The global variable name that Istanbul will use to store coverage results.	string	-
preserveComments	Indicates whether comments in the code should be preserved during the instrumentation process.	boolean	true
compact	Controls whether the output of instrumented code is compacted. Useful for debugging when set to false.	boolean	false
esModules	Determines whether the code to be instrumented uses ES Module syntax.	boolean	true
autoWrap	When set to true, wraps program code in a function to enable top-level return statements.	boolean	true
produceSourceMap	If true, instructs Istanbul to produce a source map for the instrumented code.	boolean	true
sourceMapUrlCallback	A callback function that gets invoked with the filename and the source map URL when a source map is generated.	function	-
debug	Enables the debug mode, providing additional logging information during the instrumentation process.	boolean	-

Note: If you're using TypeScript, you can import the type for the options like so:

import type { AddonOptionsWebpack } from "@storybook/addon-coverage";

The available options if your project uses Vite are as follows:

Option name	Description	Type	Default
cwd	Set the working directory	String	process.cwd()
include	See here for more info	Array<String> or string	['**']
exclude	See here for more info	Array<String> or string	list
extension	List of extensions that nyc should attempt to handle in addition to .js	Array<String> or string	['.js', '.cjs', '.mjs', '.ts', '.tsx', '.jsx', '.vue', '.svelte]
requireEnv	Optional boolean to require the environment variable (defaults to VITE_COVERAGE) to equal true in order to instrument the code. Otherwise it will instrument even if env variable is not set. However if requireEnv is not set the instrumentation will stop if the environment variable is equal to false.	boolean	-
cypress	Optional boolean to change the environment variable to CYPRESS_COVERAGE instead of VITE_COVERAGE. For ease of use with @cypress/code-coverage coverage	boolean	-
checkProd	Optional boolean to enforce the plugin to skip instrumentation for production environments. Looks at Vite's isProduction key from the ResolvedConfig.	boolean	-
forceBuildInstrument	Optional boolean to enforce the plugin to add instrumentation in build mode.	boolean	false
nycrcPath	Path to specific nyc config to use instead of automatically searching for a nycconfig. This parameter is just passed down to @istanbuljs/load-nyc-config.	string	-

Note: If you're using TypeScript, you can import the type for the options like so:

import type { AddonOptionsVite } from "@storybook/addon-coverage";

Troubleshooting

The coverage addon doesn't support optimized builds

The --test flag is designed to be as fast as possible, removing addons known to slow down the build and are not needed for functional testing. One of these addons is @storybook/addon-coverage, which is used in conjunction with the Storybook Test runner to collect coverage information for your stories.

If you are using addon-coverage AND running the test runner against your built Storybook, the --test flag will strip out the coverage information. To configure the --test build to keep coverage information (at the expense of a slightly slower build), update your Storybook configuration file (i.e.,.storybook/main.js|ts) and include the disabledAddons option.

// main.js

export default {
  // Your Storybook configuration goes here
  build: {
    test: {
      disabledAddons: [
        '@storybook/addon-docs',
        '@storybook/addon-essentials/docs',
      ],
    },
  },
}

Development scripts

• yarn start runs babel in watch mode
• yarn build build and package your addon code

To run the examples, choose one of the projects in the examples directory then run:

• yarn to install dependencies and link the addon locally
• yarn storybook to run Storybook
• yarn test-storybook --coverage to test coverage report generation

License

MIT