component-fixtures

# Component Fixtures Component fixtures render isolated UI components for visual screenshot testing via the component explorer. Fixtures live in `src/vs/workbench/test/browser/componentFixtures/` and are auto-discovered by the Vite dev server using the glob `src/**/*.fixture.ts`. Use tools `mcp_component-exp_`* to list and screenshot fixtures. If you cannot see these tools, inform the user to them on. ## Running Fixtures Locally 1. Start the component explorer server: run the **Component Explorer Server** task 2. Use the `mcp_component-exp_list_fixtures` tool to see all available fixtures and their URLs 3. Use the `mcp_component-exp_screenshot` tool to capture screenshots programmatically ## File Structure Each fixture file exports a default `defineThemedFixtureGroup(...)`. The file must end with `.fixture.ts`. ``` src/vs/workbench/test/browser/componentFixtures/ fixtureUtils.ts # Shared helpers (DO NOT import @vscode/component-explorer elsewhere) myComponent.fixture.ts # Your fixture file ``` ## Basic Pattern ```typescript import { ComponentFixtureContext, createEditorServices, defineComponentFixture, defineThemedFixtureGroup } from './fixtureUtils.js'; export default defineThemedFixtureGroup({ path: 'myFeature/' }, { Default: defineComponentFixture({ render: renderMyComponent }), AnotherVariant: defineComponentFixture({ render: renderMyComponent }), }); function renderMyComponent({ container, disposableStore, theme }: ComponentFixtureContext): void { container.style.width = '400px'; const instantiationService = createEditorServices(disposableStore, { colorTheme: theme, additionalServices: (reg) => { // Register additional services the component needs reg.define(IMyService, MyServiceImpl); reg.defineInstance(IMockService, mockInstance); }, }); const widget = disposableStore.add( instantiationService.createInstance(MyWidget, /* constructor args */) ); container.appendChild(widget.domNode); } ``` Key points: - **`defineThemedFixtureGroup`** automatically creates Dark and Light variants for each fixture - **`defineComponentFixture`** wraps your render function with theme setup, async readiness, and disposable management - **`createEditorServices`** provides a `TestInstantiationService` with base editor services pre-registered - Always register created widgets with `disposableStore.add(...)` to prevent leaks - Pass `colorTheme: theme` to `createEditorServices` so theme colors render correctly ### File icon themes Fixtures use Seti file icons by default. Select another built-in theme, or disable file icons, on the individual fixture: ```typescript defineComponentFixture({ fileIconTheme: 'vs-minimal', render: renderMyComponent }); defineComponentFixture({ fileIconTheme: 'none', render: renderMyComponent }); ``` When the rendered component reads `IThemeService`, pass the selected theme from `ComponentFixtureContext` to `createEditorServices`: ```typescript function renderMyComponent({ disposableStore, theme, fileIconTheme }: ComponentFixtureContext): void { const instantiationService = createEditorServices(disposableStore, { colorTheme: theme, fileIconTheme, }); } ``` ## Utilities from fixtureUtils.ts | Export | Purpose | |---|---| | `defineComponentFixture` | Creates Dark/Light themed fixture variants from a render function | | `defineThemedFixtureGroup` | Groups multiple themed fixtures into a named fixture group | | `createEditorServices` | Creates `TestInstantiationService` with all base editor services | | `registerWorkbenchServices` | Registers additional workbench services (context menu, label, etc.) | | `createTextModel` | Creates a text model via `ModelService` for editor fixtures | | `setupTheme` | Applies theme CSS to a container (called automatically by `defineComponentFixture`) | | `darkTheme` / `lightTheme` | Pre-loaded `ColorThemeData` instances | **Important:** Only `fixtureUtils.ts` may import from `@vscode/component-explorer`. All fixture files must go through the helpers in `fixtureUtils.ts`. ## CSS Scoping Fixtures share the document and workbench stylesheets (`isolation: 'none'`). The helpers scope theme and file-icon styles, but DOM, CSS, and process-wide registrations are not isolated automatically. ### Shared theme initialization `fixtureUtilsCss.ts` loads the shared workbench color and size registrations before generating and caching theme CSS, including the agent tokens in `vs/workbench/common/agentsColors.ts` and `agentsSizes.ts`. Keep required product-wide registrations in this shared bootstrap, not in individual fixtures: discovering another fixture must not change an existing fixture's typography or colors. Reuse lightweight registration modules from the owning shared layer rather than importing product entry points or higher-layer contributions. ### Matching production CSS selectors Many VS Code components have CSS rules scoped to deep ancestor selectors (e.g., `.interactive-session .interactive-input-part > .widget-container .my-element`). In fixtures, you must recreate the required ancestor DOM structure for these selectors to match: ```typescript function render({ container }: ComponentFixtureContext): void { container.classList.add('interactive-session'); // Recreate ancestor structure that CSS selectors expect const inputPart = dom.$('.interactive-input-part'); const widgetContainer = dom.$('.widget-container'); inputPart.appendChild(widgetContainer); container.appendChild(inputPart); widgetContainer.appendChild(myWidget.domNode); } ``` **Design recommendation for new components:** Avoid deeply nested CSS selectors that require specific ancestor elements. Use self-contained class names (e.g., `.my-widget .my-element` rather than `.parent-view .parent-part > .wrapper .my-element`). This makes components easier to fixture and reuse. ## Services ### Using createEditorServices `createEditorServices` pre-registers these services: `IAccessibilityService`, `IKeybindingService`, `IClipboardService`, `IOpenerService`, `INotificationService`, `IDialogService`, `IUndoRedoService`, `ILanguageService`, `IConfigurationService`, `IStorageService`, `IThemeService`, `IModelService`, `ICodeEditorService`, `IContextKeyService`, `ICommandService`, `ITelemetryService`, `IHoverService`, `IUserInteractionService`, and more. ### Additional services Register extra services via `additionalServices`: ```typescript createEditorServices(disposableStore, { additionalServices: (reg) => { // Class-based (instantiated by DI): reg.define(IMyService, MyServiceImpl); // Instance-based (pre-constructed): reg.defineInstance(IMyService, myMockInstance); }, }); ``` ### Mocking services Use the `mock<T>()` helper from `base/test/common/mock.js` to create mock service instances: ```typescript import { mock } from '../../../../base/test/common/mock.js'; const myService = new class extends mock<IMyService>() { override someMethod(): string { return 'test'; } override onSomeEvent = Event.None; }; reg.defineInstance(IMyService, myService); ``` For mock view models or data objects: ```typescript const element = new class extends mock<IChatRequestViewModel>() { }(); ``` ## Async Rendering The component explorer awaits the render promise, then waits two animation frames. Those frames are not a readiness guarantee for image decoding, native resize observers, delayed layout, or scrollbar idle timers. The render promise must resolve only when the fixture represents its named state: - Await assets that affect the screenshot. An editor's `setInput()` may return before its main image or thumbnails have loaded; wait for the expected image count and await `decode()`, failing on missing or broken images. - Finish layout-changing actions before positioning the viewport. Wait for content height, scroll height, scroll position, and finite animations to settle, then scroll and settle again. Assert that an "offscreen" header is actually offscreen and a "visible" header is not covered by sticky content. - Account for transient visuals such as auto-hiding scrollbars. A stable height does not mean a stable screenshot. - Supply deterministic display data through existing services/options, such as a single custom thinking phrase. A seeded random generator alone does not make labels independent of render order or async callback order. - Use bounded, condition-based waits that throw on failure, not fixed sleeps or extra frames that silently accept an incomplete state. Design fixtures as **state + local inputs + an explicit readiness condition**. Supply local account icons instead of letting a mock fall back to a live avatar URL, and await decoding; `waitForFixtureCondition` polls native browser frames while preserving the virtual clock. Prefer shared DOM spinners over animated SVG backgrounds: ancestor CSS cannot stop animations inside an image. Wait for auto-hiding scrollbars to reach their intended idle state, not merely for content height to stabilize. Fixtures that depend on native browser image decoding or resize/scroll callbacks can use `virtualTime: { enabled: false }` and explicitly await those operations. Virtual JavaScript time does not advance the browser's image decoder or layout pipeline. For async fixtures with paint-order-sensitive edges, `deferPaint: true` keeps the headless fixture transparent until rendering has finished, without changing its layout or interactive preview. It prevents intermediate paints from affecting the final rasterization; it does **not** replace awaiting readiness. ### Validating fixtures Do not add automated tests whose subject is fixtures or fixture infrastructure (including fixture-only unit, Playwright, and screenshot-stability tests). Validate fixture changes with the existing Component Explorer rendering, screenshot, stability, and error tools, plus direct inspection or temporary browser probes. Ordinary tests for production behavior belong at the owning production API. Validate at the same readiness boundary CI uses: capture immediately after the headless `renderFixture()` resolves, after idle callbacks, and after remounting following another fixture. Compare exact hashes on the same platform and separately inspect the intended state; do not commit the temporary probes as fixture tests. ### Pitfall: DOM reparenting causes flickering Avoid moving rendered widgets between DOM parents after initial render. This causes: - Layout recalculation (the widget jumps as `position: absolute` coordinates become invalid) - Focus loss (blur events can trigger hide logic in widgets like QuickInput) - Screenshot instability (the component explorer may capture an intermediate layout state) **Bad pattern — reparenting a widget after async wait:** ```typescript async function render({ container }: ComponentFixtureContext): Promise<void> { const host = document.createElement('div'); container.appendChild(host); // ... create widget inside host ... await waitForWidget(); container.appendChild(widget); // BAD: reparenting causes flicker host.remove(); } ``` **Better pattern — render in-place with the correct DOM structure from the start:** ```typescript function render({ container }: ComponentFixtureContext): void { // Set up the correct DOM structure first, then create the widget inside it const widget = createWidget(container); container.appendChild(widget.domNode); } ``` If the component absolutely requires async setup (e.g., QuickInput which renders internally), minimize DOM manipulation after the widget appears by structuring the host container to match the final layout from the beginning. ## Adapting Existing Components for Fixtures Existing components often need small changes to become fixturable. When writing a fixture reveals friction, fix the component — don't work around it in the fixture. Common adaptations: ### Decouple CSS from ancestor context If a component's CSS only works inside a deeply nested selector like `.workbench .sidebar .my-view .my-widget`, refactor the CSS to be self-contained. Move the styles so they're scoped to the component's own root class: ```css /* Before: requires specific ancestors */ .workbench .sidebar .my-view .my-widget .header { font-weight: bold; } /* After: self-contained */ .my-widget .header { font-weight: bold; } ``` If the component shares styles with its parent (e.g., inheriting background color), use CSS custom properties rather than relying on ancestor selectors. ### Extract hard-coded service dependencies If a component reaches into singletons or global state instead of using DI, refactor it to accept services through the constructor: ```typescript // Before: hard to mock in fixtures class MyWidget { private readonly config = getSomeGlobalConfig(); } // After: injectable and testable class MyWidget { constructor(@IConfigurationService private readonly configService: IConfigurationService) { } } ``` ### Add options to control auto-focus and animation Components that auto-focus on creation or run animations cause flaky screenshots. Add an options parameter: ```typescript interface IMyWidgetOptions { shouldAutoFocus?: boolean; } ``` The fixture passes `shouldAutoFocus: false`. The production call site keeps the default behavior. ### Expose internal state for "already completed" rendering Many components have lifecycle states (loading → active → completed). If the component can only reach the "completed" state through user interaction, add support for initializing directly into that state via constructor data: ```typescript // The fixture can pass pre-filled data to render the summary/completed state // without simulating the full user interaction flow. const carousel: IChatQuestionCarousel = { questions, allowSkip: true, kind: 'questionCarousel', isUsed: true, // Already completed data: { 'q1': 'answer' }, // Pre-filled answers }; ``` ### Make DOM node accessible If a component builds its DOM internally and doesn't expose the root element, add a public `readonly domNode: HTMLElement` property so fixtures can append it to the container. ### Keep test-only operations out of the production API When a fixture or test must drive state that production reaches only through user input or services (for example focusing, selecting, or collapsing rows, or locating a rendered row), don't add public methods for it: other code will start calling them and bypass the real flows. Make the minimum `protected` and implement the operations in a test-only subclass under `test/` (such as `TestSessionsList extends SessionsList`), which product code cannot import. ## Writing Fixture-Friendly Components When designing new UI components, follow these practices to make them easy to fixture: ### 1. Accept a container element in the constructor ```typescript // Good: container is passed in class MyWidget { constructor(container: HTMLElement, @IFoo foo: IFoo) { this.domNode = dom.append(container, dom.$('.my-widget')); } } // Also good: widget creates its own domNode for the caller to place class MyWidget { readonly domNode: HTMLElement; constructor(@IFoo foo: IFoo) { this.domNode = dom.$('.my-widget'); } } ``` ### 2. Use dependency injection for all services All external dependencies should come through DI so fixtures can provide test implementations: ```typescript // Good: services injected constructor(@IThemeService private readonly themeService: IThemeService) { } // Bad: reaching into globals constructor() { this.theme = getGlobalTheme(); } ``` ### 3. Keep CSS selectors shallow ```css /* Good: self-contained, easy to fixture */ .my-widget .my-header { ... } .my-widget .my-list-item { ... } /* Bad: requires deep ancestor chain */ .workbench .sidebar .my-view .my-widget .my-header { ... } ``` ### 4. Avoid reading from layout/window services during construction Components that measure the window or read layout dimensions during construction are hard to fixture because the shadow DOM container has different dimensions than the workbench: ```typescript // Prefer: use CSS for sizing, or accept dimensions as parameters container.style.width = '400px'; container.style.height = '300px'; // Avoid: reading from layoutService during construction const width = this.layoutService.mainContainerDimension.width; ``` ### 5. Support disabling auto-focus in fixtures Auto-focus can interfere with screenshot stability. Provide options to disable it: ```typescript interface IMyWidgetOptions { shouldAutoFocus?: boolean; // Fixtures pass false } ``` ### 6. Expose the DOM node The fixture needs to append the widget's DOM to the container. Expose it as a public `readonly domNode: HTMLElement`. ### 7. Make hover and focus states renderable Fixtures cannot trigger CSS `:hover`, and DOM focus is only deterministic through `ctx.focus()`. Keep interaction-dependent visuals reachable from state: - Pair every `:hover` selector a visual depends on with a `.hovered` class, e.g. `.monaco-list-row:is(:hover, .hovered)`; `:is()` keeps specificity unchanged. List widgets already style `.monaco-list-row.hovered` like a hovered row. - Drive focus and selection through the component (list rows get `.focused` and `.selected` from the list traits), from a test-only subclass when production has no such API (see [Keep test-only operations out of the production API](#keep-test-only-operations-out-of-the-production-api)). Then call `ctx.focus()` when the state needs DOM focus. - When JavaScript also reacts to hover (for example `mouseover` listeners), dispatch a `mouseover` on the element as well as adding `.hovered`. `src/vs/sessions/contrib/sessions/test/browser/sessionsListFixtureUtils.ts` renders `interaction: { hovered, focused, selected }` this way. ## Multiple Fixture Variants Create variants to show different states of the same component: ```typescript export default defineThemedFixtureGroup({ // Different data states Empty: defineComponentFixture({ render: (ctx) => renderWidget(ctx, { items: [] }) }), WithItems: defineComponentFixture({ render: (ctx) => renderWidget(ctx, { items: sampleItems }) }), // Different configurations ReadOnly: defineComponentFixture({ render: (ctx) => renderWidget(ctx, { readonly: true }) }), Editable: defineComponentFixture({ render: (ctx) => renderWidget(ctx, { readonly: false }) }), // Lifecycle states