Enable test coverage for playwright tests.

test/coverage.ts

@@ -0,0 +1,68 @@
+/**
+ * Custom Playwright fixture that collects Istanbul code coverage after each test.
+ *
+ * When the app is built with COVERAGE=1 (which enables babel-plugin-istanbul),
+ * the bundled code exposes `window.__coverage__`. This fixture grabs that object
+ * after every test and writes it to `.nyc_output/` so `nyc report` can merge and
+ * render a coverage report.
+ *
+ * Usage: In spec files, replace
+ *   import { test, expect } from "@playwright/test";
+ * with
+ *   import { test, expect } from "../coverage";   // adjust relative path
+ */
+import { test as base, Browser, expect, Frame, Locator, Page } from "@playwright/test";
+import * as crypto from "crypto";
+import * as fs from "fs";
+import * as path from "path";
+
+const nycOutputDir = path.join(__dirname, "..", ".nyc_output");
+
+/**
+ * Try to pull `window.__coverage__` from every frame in the page.
+ * The app loads inside an iframe in testExplorer.html, so we check
+ * both the main page and all child frames.
+ */
+async function collectCoverage(page: Page): Promise<Record<string, unknown> | null> {
+  // Try main frame first
+  try {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const cov = await page.evaluate(() => (window as Record<string, any>).__coverage__);
+    if (cov && Object.keys(cov).length > 0) {
+      return cov as Record<string, unknown>;
+    }
+  } catch {
+    // page may have been closed already
+  }
+
+  // Try child frames (the explorer often runs inside an iframe)
+  for (const frame of page.frames()) {
+    try {
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      const cov = await frame.evaluate(() => (window as Record<string, any>).__coverage__);
+      if (cov && Object.keys(cov).length > 0) {
+        return cov as Record<string, unknown>;
+      }
+    } catch {
+      // frame may be detached
+    }
+  }
+
+  return null;
+}
+
+const test = base.extend({
+  page: async ({ page }, use) => {
+    await use(page);
+
+    const coverage = await collectCoverage(page);
+    if (coverage) {
+      fs.mkdirSync(nycOutputDir, { recursive: true });
+      const id = crypto.randomBytes(8).toString("hex");
+      fs.writeFileSync(path.join(nycOutputDir, `coverage-${id}.json`), JSON.stringify(coverage));
+    }
+  },
+});
+
+export { Browser, expect, Frame, Locator, Page, test };
+export type { Page as PageType };