feat: add test for markdown webview (#5740)

* feat: add test for markdown webview

* fixup!: use frameLocator

test/e2e/webview.test.ts

@@ -0,0 +1,28 @@
+import { promises as fs } from "fs"
+import * as path from "path"
+import { describe, test, expect } from "./baseFixture"
+
+describe("Webviews", ["--disable-workspace-trust"], {}, () => {
+  test("should preview a Markdown file", async ({ codeServerPage }) => {
+    // Create Markdown file
+    const heading = "Hello world"
+    const dir = await codeServerPage.workspaceDir
+    const file = path.join(dir, "text.md")
+    await fs.writeFile(file, `# ${heading}`)
+    await codeServerPage.openFile(file)
+
+    // Open Preview
+    await codeServerPage.executeCommandViaMenus("Markdown: Open Preview to the Side")
+    // Wait for the iframe to open and load
+    await codeServerPage.waitForTab(`Preview ${file}`)
+
+    // It's an iframe within an iframe
+    // so we have to do .frameLocator twice
+    const renderedText = await codeServerPage.page
+      .frameLocator("iframe.webview.ready")
+      .frameLocator("#active-frame")
+      .locator("text=Hello world")
+
+    expect(renderedText).toBeVisible
+  })
+})