feat: support DOM snapshot testing

.storybook/main.js

@@ -11,7 +11,7 @@ const stories = [
     directory: '../stories/molecules',
   },
   // general glob
-  '../stories/pages/**/*.stories.*',
+  '../stories/pages/**/*.stories.@(js|jsx|ts|tsx)',
 ];
 
 if (process.env.STRESS_TEST) {

.storybook/test-runner.ts

@@ -9,13 +9,19 @@ const config: TestRunnerConfig = {
     expect.extend({ toMatchImageSnapshot });
   },
   async postRender(page, context) {
+    // Visual snapshot tests
     const image = await page.screenshot({ fullPage: true });
     expect(image).toMatchImageSnapshot({
       customSnapshotsDir,
       customSnapshotIdentifier: context.id,
       failureThreshold: 0.03,
       failureThresholdType: 'percent',
     });
+
+    const elementHandler = await page.$('#root');
+    const innerHTML = await elementHandler.innerHTML();
+    // HTML snapshot tests
+    expect(innerHTML).toMatchSnapshot();
   },
 };
 

README.md

@@ -19,8 +19,8 @@ Read the announcement: [Interaction Testing with Storybook](https://storybook.js
   - [Image snapshot recipe](#image-snapshot-recipe)
   - [Render lifecycle](#render-lifecycle)
 - [Troubleshooting](#troubleshooting)
-    - [The test runner seems flaky and keeps timing out](#the-test-runner-seems-flaky-and-keeps-timing-out)
-    - [Adding the test runner to other CI environments](#adding-the-test-runner-to-other-ci-environments)
+  - [The test runner seems flaky and keeps timing out](#the-test-runner-seems-flaky-and-keeps-timing-out)
+  - [Adding the test runner to other CI environments](#adding-the-test-runner-to-other-ci-environments)
 - [Future work](#future-work)
 
 ## Features
@@ -170,7 +170,7 @@ module.exports = {
 };
 ```
 
-Once you have a valid `stories.json` file, your Storybook will be compatible with the "stories.json mode". 
+Once you have a valid `stories.json` file, your Storybook will be compatible with the "stories.json mode".
 
 By default, the test runner will detect whether your Storybook URL is local or remote, and if it is remote, it will run in "stories.json mode" automatically. To disable it, you can pass the `--no-stories-json` flag:
 
@@ -265,9 +265,25 @@ All three functions can be set up in the configuration file `.storybook/test-run
 
 > **NOTE:** These test hooks are experimental and may be subject to breaking changes. We encourage you to test as much as possible within the story's play function.
 
+### DOM snapshot recipe
+
+The `postRender` function provides a [Playwright page](https://playwright.dev/docs/api/class-page) instance, of which you can use for DOM snapshot testing:
+
+```js
+// .storybook/test-runner.js
+module.exports = {
+  async postRender(page, context) {
+    // the #root element wraps the story
+    const elementHandler = await page.$('#root');
+    const innerHTML = await elementHandler.innerHTML();
+    expect(innerHTML).toMatchSnapshot();
+  },
+};
+```
+
 ### Image snapshot recipe
 
-Consider, for example, the following recipe to take image snapshots:
+Here's a slightly different recipe for image snapshot testing:
 
 ```js
 // .storybook/test-runner.js

package.json

@@ -102,6 +102,7 @@
     "global": "^4.4.0",
     "is-localhost-ip": "^1.4.0",
     "jest-playwright-preset": "^1.7.0",
+    "jest-serializer-html": "^7.1.0",
     "jest-watch-typeahead": "^1.0.0",
     "node-fetch": "^2",
     "playwright": "^1.14.0",

src/config/jest-playwright.ts

@@ -14,6 +14,7 @@ export const getJestConfig = () => {
     globalTeardown: '@storybook/test-runner/playwright/global-teardown.js',
     testEnvironment: '@storybook/test-runner/playwright/custom-environment.js',
     setupFilesAfterEnv: ['@storybook/test-runner/playwright/jest-setup.js'],
+    snapshotSerializers: ['jest-serializer-html'],
     testEnvironmentOptions: {
       'jest-playwright': {
         browsers: TEST_BROWSERS.split(',')

stories/atoms/__snapshots__/Button.stories.js.snap

@@ -0,0 +1,39 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Atoms/Button Demo play-test 2`] = `
+<button type="button">
+  Click
+</button>
+`;
+
+exports[`Atoms/Button FindBy play-test 2`] = `
+<button type="button">
+  Loaded!
+</button>
+`;
+
+exports[`Atoms/Button Primary smoke-test 2`] = `
+<button type="button"
+        class="storybook-button storybook-button--medium storybook-button--primary"
+>
+  Button
+</button>
+`;
+
+exports[`Atoms/Button WaitFor play-test 2`] = `
+<button type="button">
+  Click
+</button>
+`;
+
+exports[`Atoms/Button WaitForElementToBeRemoved play-test 2`] = `
+<button type="button">
+  Loaded!
+</button>
+`;
+
+exports[`Atoms/Button WithLoaders play-test 2`] = `
+<button type="button">
+  Todo: delectus aut autem
+</button>
+`;

stories/molecules/__snapshots__/Header.stories.js.snap

@@ -0,0 +1,88 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Molecules/Header LoggedIn smoke-test 2`] = `
+<header>
+  <div class="wrapper">
+    <div>
+      <svg width="32"
+           height="32"
+           viewbox="0 0 32 32"
+           xmlns="http://www.w3.org/2000/svg"
+      >
+        <g fill="none"
+           fill-rule="evenodd"
+        >
+          <path d="M10 0h12a10 10 0 0110 10v12a10 10 0 01-10 10H10A10 10 0 010 22V10A10 10 0 0110 0z"
+                fill="#FFF"
+          >
+          </path>
+          <path d="M5.3 10.6l10.4 6v11.1l-10.4-6v-11zm11.4-6.2l9.7 5.5-9.7 5.6V4.4z"
+                fill="#555AB9"
+          >
+          </path>
+          <path d="M27.2 10.6v11.2l-10.5 6V16.5l10.5-6zM15.7 4.4v11L6 10l9.7-5.5z"
+                fill="#91BAF8"
+          >
+          </path>
+        </g>
+      </svg>
+      <h1>
+        Acme
+      </h1>
+    </div>
+    <div>
+      <button type="button"
+              class="storybook-button storybook-button--small storybook-button--secondary"
+      >
+        Log out
+      </button>
+    </div>
+  </div>
+</header>
+`;
+
+exports[`Molecules/Header LoggedOut smoke-test 2`] = `
+<header>
+  <div class="wrapper">
+    <div>
+      <svg width="32"
+           height="32"
+           viewbox="0 0 32 32"
+           xmlns="http://www.w3.org/2000/svg"
+      >
+        <g fill="none"
+           fill-rule="evenodd"
+        >
+          <path d="M10 0h12a10 10 0 0110 10v12a10 10 0 01-10 10H10A10 10 0 010 22V10A10 10 0 0110 0z"
+                fill="#FFF"
+          >
+          </path>
+          <path d="M5.3 10.6l10.4 6v11.1l-10.4-6v-11zm11.4-6.2l9.7 5.5-9.7 5.6V4.4z"
+                fill="#555AB9"
+          >
+          </path>
+          <path d="M27.2 10.6v11.2l-10.5 6V16.5l10.5-6zM15.7 4.4v11L6 10l9.7-5.5z"
+                fill="#91BAF8"
+          >
+          </path>
+        </g>
+      </svg>
+      <h1>
+        Acme
+      </h1>
+    </div>
+    <div>
+      <button type="button"
+              class="storybook-button storybook-button--small storybook-button--secondary"
+      >
+        Log in
+      </button>
+      <button type="button"
+              class="storybook-button storybook-button--small storybook-button--primary"
+      >
+        Sign up
+      </button>
+    </div>
+  </div>
+</header>
+`;