Add screenshot tests

.gitignore

@@ -20,3 +20,9 @@ Thumbs.db
 # Vite
 vite.config.js.timestamp-*
 vite.config.ts.timestamp-*
+
+# Playwright
+/test-results/
+/playwright-report/
+/blob-report/
+/playwright/.cache/

package.json

@@ -12,6 +12,11 @@
         "check:svader": "cd packages/svader && npm run check",
         "check:tests-svelte4": "cd packages/tests-svelte4 && npm run check",
         "build": "npm run package && npm run build:tests-svelte4",
-        "build:tests-svelte4": "cd packages/tests-svelte4 && npm run build"
+        "build:tests-svelte4": "cd packages/tests-svelte4 && npm run build",
+        "test": "playwright test"
+    },
+    "devDependencies": {
+        "@playwright/test": "^1.48.1",
+        "@types/node": "^22.7.9"
     }
 }

playwright.config.ts

@@ -0,0 +1,89 @@
+import { defineConfig, devices } from '@playwright/test';
+
+// Apparently, Chromium browsers need to be explicitly told to use GPU acceleration in headless mode,
+// and software rendering creates slightly different results for WebGL in noise and such,
+// while WebGPU has no software fallback at all.
+const chromiumHardware = {
+  args: [
+    "--enable-gpu",
+  ],
+};
+
+/**
+ * See https://playwright.dev/docs/test-configuration.
+ */
+export default defineConfig({
+  testDir: './tests',
+  snapshotPathTemplate: '{testDir}/.generated-screenshots/{testFilePath}/{arg}{ext}',
+  /* Run tests in files in parallel */
+  fullyParallel: true,
+  /* Fail the build on CI if you accidentally left test.only in the source code. */
+  forbidOnly: !!process.env.CI,
+  /* Retry on CI only */
+  retries: process.env.CI ? 2 : 0,
+  /* Opt out of parallel tests on CI. */
+  workers: process.env.CI ? 1 : undefined,
+  /* Reporter to use. See https://playwright.dev/docs/test-reporters */
+  reporter: 'html',
+  /* Shared settings for all the projects below. See https://playwright.dev/docs/api/class-testoptions. */
+  use: {
+    /* Collect trace when retrying the failed test. See https://playwright.dev/docs/trace-viewer */
+    trace: 'on-first-retry',
+
+    contextOptions: {
+      // Disable animations so screenshots are comparable
+      reducedMotion: 'reduce',
+    },
+  },
+
+  projects: [
+    {
+      name: 'Firefox',
+      use: {
+        ...devices['Desktop Firefox'],
+      },
+    },
+    {
+      name: 'Microsoft Edge',
+      use: { 
+        ...devices['Desktop Edge'], 
+        channel: 'msedge',
+        launchOptions: chromiumHardware,
+      },
+    },
+    {
+      name: 'Google Chrome',
+      use: {
+        ...devices['Desktop Chrome'], 
+        channel: 'chrome',
+        launchOptions: chromiumHardware,
+      },
+    },
+    /* TODO: Test these as well */
+    // {
+    //     name: 'Chromium',
+    //     use: {
+    //       ...devices['Desktop Chrome'],
+    //       launchOptions: chromiumHardware,
+    //     },
+    //   },
+    // {
+    //   name: 'WebKit',
+    //   use: { ...devices['Desktop Safari'] },
+    // },
+    // {
+    //   name: 'Mobile Chrome',
+    //   use: { ...devices['Pixel 5'] },
+    // },
+    // {
+    //   name: 'Mobile Safari',
+    //   use: { ...devices['iPhone 12'] },
+    // },
+  ],
+
+  webServer: {
+    command: 'npm run preview:v4',
+    port: 4173,
+    reuseExistingServer: !process.env.CI,
+  },
+});

tests/svelte4.spec.ts

@@ -0,0 +1,113 @@
+import { test, expect, TestInfo, Page } from "@playwright/test";
+
+// No output on the console is desired
+test.beforeEach(async ({ page }) => {
+    page.on("console", (msg) => {
+        throw new Error(`Output printed to console:\n${msg.text()}`);
+    });
+});
+
+/** Project names (as defined in playwright.config.ts) that are not expected to support WebGPU. */
+const webGpuUnsupported = [
+    "Firefox",
+]
+
+/**
+ * Takes a screenshot of the current page and compares it to a reference, as indexed by the given arguments.
+ * If a reference screenshot does not exist, it will be created and used for future assertions. 
+ * 
+ * @param page
+ * @param info
+ * @param name A name that identifies this test.
+ * @param api The API used in the test, either `"webgl"` or `"webgpu"`.
+ * @param number A number identifying the specific screeenshot within the test, if multiple are included.
+ */
+async function assertScreenshot(page: Page, info: TestInfo, name: string, api: "webgl" | "webgpu", number?: number) {
+    const projectName = info.project.name;
+    const isMobile = info.project.use.isMobile ?? false;
+
+    const mobileString = isMobile ? "-mobile" : "";
+    const numberString = number ? `-${number}` : "";
+
+    const isWebGpu = api === "webgpu";
+    const isWebGpuUnsupported = webGpuUnsupported.includes(projectName);
+    const unsupportedString = (isWebGpu && isWebGpuUnsupported) ? "-unsupported" : "";
+
+    const fileName = `${name}-${api}${unsupportedString}${mobileString}${numberString}.png`;
+
+    await expect.soft(page).toHaveScreenshot(fileName, {
+        // Allow for slightly different rendering on different platforms,
+        // since Chrome and Firefox have slightly different text-rendering and inputs etc.
+        maxDiffPixelRatio: 0.01,
+    });
+}
+
+const apis = ["webgl", "webgpu"] as const;
+apis.forEach(api => {
+
+    test(`Hello world [${api}]`, async ({ page }, info) => {
+        const pageName = "hello-world";
+
+        await page.goto(`/${pageName}/${api}`);
+        await assertScreenshot(page, info, pageName, api);
+    });
+
+    test(`Remounting canvas [${api}]`, async ({ page }, info) => {
+        const pageName = "remount";
+
+        await page.goto(`/${pageName}/${api}`);
+        let show = page.getByLabel("Show")
+        await show.uncheck();
+        await assertScreenshot(page, info, pageName, api, 1);
+        for (let i = 0; i < 10; i++) {
+            await show.check();
+            await show.uncheck();
+        }
+        await show.check();
+        await assertScreenshot(page, info, pageName, api, 2);
+    });
+
+    test(`Oversized canvas [${api}]`, async ({ page }, info) => {
+        const pageName = "oversized-canvas";
+
+        await page.goto(`/${pageName}/${api}`);
+        await assertScreenshot(page, info, pageName, api, 1);
+        // Scroll to bottom-right corner
+        await page.evaluate(() => window.scrollBy(document.body.scrollWidth, document.body.scrollHeight));
+        await assertScreenshot(page, info, pageName, api, 2);
+    });
+
+    test(`Logo [${api}]`, async ({ page }, info) => {
+        const pageName = "logo";
+
+        await page.goto(`/${pageName}/${api}`);
+        await assertScreenshot(page, info, pageName, api);
+    });
+
+    test(`Landing page with bubbles [${api}]`, async ({ page }, info) => {
+        const pageName = "landing-page-bubbles";
+
+        await page.goto(`/${pageName}/${api}`);
+        await assertScreenshot(page, info, pageName, api);
+    });
+
+    test(`Landing page with a halo [${api}]`, async ({ page }, info) => {
+        const pageName = "landing-page-halo";
+
+        await page.goto(`/${pageName}/${api}`);
+        await assertScreenshot(page, info, pageName, api);
+    });
+
+    test(`Slider component [${api}]`, async ({ page }, info) => {
+        const pageName = "slider";
+
+        await page.goto(`/${pageName}/${api}`);
+        const slider = page.getByRole("slider");
+        await assertScreenshot(page, info, pageName, api, 1);
+        slider.fill("1");
+        await assertScreenshot(page, info, pageName, api, 2);
+        slider.fill("0");
+        await assertScreenshot(page, info, pageName, api, 3);
+    });
+
+});

tsconfig.json

@@ -0,0 +1,6 @@
+{
+    "compilerOptions": {
+        "types": ["node"],
+        "strict": true,
+    }
+}