feat: add auto-fixture for Istanbul E2E coverage collection

- Adds _coverageCollector automatic fixture to test object
- Collects window.__coverage__ from browser after each test
- Writes per-test JSON files to <outputDir>/coverage/
- Enabled via E2E_COLLECT_COVERAGE=1
- Zero overhead when disabled (no page.evaluate or fs operations)
- Designed for use with instrumented dynamic plugin builds

This enables automatic E2E coverage collection for all workspaces
in rhdh-plugin-export-overlays without modifying any test files.

Author: gustavolira

docs/changelog.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 
 ## [1.1.45] - Current
 
+### Added
+
+- **E2E coverage collection auto-fixture**: New `_coverageCollector` automatic fixture collects Istanbul coverage (`window.__coverage__`) from the browser after each test and writes per-test JSON files to `<outputDir>/coverage/`. Enabled via `E2E_COLLECT_COVERAGE=true`. Zero overhead when disabled — no `page.evaluate` call or fs operations. Designed for use with instrumented dynamic plugin builds (nyc instrument).
+
 ### Fixed
 
 - **`default.packages.yaml` fetch URL**: `release-1.10` continues to fetch from the `rhdh` repo; all other branches (including `main`) now fetch from `rhdh-plugin-export-overlays` where the file was moved.

src/playwright/fixtures/test.ts

@@ -4,13 +4,16 @@ import { LoginHelper, UIhelper } from "../helpers/index.js";
 import { runOnce } from "../run-once.js";
 import { $ } from "../../utils/bash.js";
 import { WorkspacePaths } from "../../utils/workspace-paths.js";
+import fs from "node:fs";
 import path from "path";
 
 type RHDHDeploymentTestFixtures = {
   rhdh: RHDHDeployment;
   uiHelper: UIhelper;
   loginHelper: LoginHelper;
   autoAnnotations: void;
+  // eslint-disable-next-line @typescript-eslint/naming-convention
+  _coverageCollector: void;
 };
 
 type RHDHDeploymentWorkerFixtures = {
@@ -77,6 +80,34 @@ const baseTest = base.extend<
     },
     { auto: true, scope: "test" },
   ],
+  // eslint-disable-next-line @typescript-eslint/naming-convention
+  _coverageCollector: [
+    async ({ page }, use, testInfo) => {
+      await use();
+      if (process.env.E2E_COLLECT_COVERAGE !== "true") return;
+      try {
+        const coverage = await page.evaluate(
+          () =>
+            (
+              globalThis as unknown as {
+                // eslint-disable-next-line @typescript-eslint/naming-convention
+                __coverage__?: Record<string, unknown>;
+              }
+            ).__coverage__,
+        );
+        if (!coverage) return;
+        const dir = path.join(testInfo.project.outputDir, "coverage");
+        fs.mkdirSync(dir, { recursive: true });
+        fs.writeFileSync(
+          path.join(dir, `${testInfo.testId}-${Date.now()}.json`),
+          JSON.stringify(coverage),
+        );
+      } catch {
+        // Best-effort: page may have crashed or been closed
+      }
+    },
+    { auto: true, scope: "test" },
+  ],
 });
 
 export const test = Object.assign(baseTest, {