Adding example for test coverage using istanbul

package.json

@@ -7,6 +7,7 @@
     "node": ">=22"
   },
   "scripts": {
+    "pretest": "tsc --incremental -p tsconfig.json",
     "start": "API_MODE=msw vite",
     "start:msw": "API_MODE=msw vite",
     "start:nexus": "API_MODE=nexus vite",
@@ -49,6 +50,7 @@
     "@tanstack/react-table": "^8.20.5",
     "@xterm/addon-fit": "^0.10.0",
     "@xterm/xterm": "^5.5.0",
+    "babel-plugin-istanbul": "^7.0.1",
     "classnames": "^2.5.1",
     "date-fns": "^3.6.0",
     "filesize": "^10.1.6",
@@ -77,6 +79,7 @@
     "tunnel-rat": "^0.1.2",
     "use-debounce": "^10.0.4",
     "uuid": "^10.0.0",
+    "v8-to-istanbul": "^9.3.0",
     "zod": "^4.0.17",
     "zustand": "^5.0.3"
   },

test/e2e/action-menu.e2e.ts

@@ -5,10 +5,12 @@
  *
  * Copyright Oxide Computer Company
  */
-import { expect, test, type Page } from '@playwright/test'
+import { type Page } from '@playwright/test'
 
+import { expect, test } from './fixtures'
 import { expectNotVisible } from './utils'
 
+
 const openActionMenu = async (page: Page) => {
   // open the action menu (use the sidenav button, as keyboard events aren't reliable in Playwright)
   await page.getByRole('button', { name: 'JUMP TO' }).click()

test/e2e/fixtures.ts

@@ -0,0 +1,44 @@
+import { mkdirSync, writeFileSync } from 'fs'
+import { resolve } from 'path'
+import { test as base } from '@playwright/test'
+import v8toIstanbul from 'v8-to-istanbul'
+
+const baseURL = 'http://localhost:4009'
+
+export const test = base.extend({
+  collectCoverage: [
+    async ({ page }, use) => {
+      await page.coverage.startJSCoverage()
+
+      await use(null)
+
+      const coverage = await page.coverage.stopJSCoverage()
+      mkdirSync('.nyc_output', { recursive: true })
+
+      const allCoverage: Record<string, any> = {}
+
+      for (const entry of coverage) {
+        const localPath = entry.url.replace(baseURL, '').split('?')[0]
+        const cleanPath = localPath.startsWith('/') ? localPath.slice(1) : localPath
+        const filePath = resolve(cleanPath)
+
+        const converter = v8toIstanbul(filePath)
+        try {
+          await converter.load()
+          converter.applyCoverage(entry.functions)
+          Object.assign(allCoverage, converter.toIstanbul())
+        } catch (e) {
+          console.warn(
+            `Failed to convert coverage for ${filePath}:`,
+            e instanceof Error ? e.message : String(e)
+          )
+        }
+      }
+
+      writeFileSync(resolve('.nyc_output/coverage.json'), JSON.stringify(allCoverage))
+    },
+    { auto: true },
+  ],
+})
+
+export { expect } from '@playwright/test'