refactor: encapsulate Metro startup orchestration

packages/bundler-metro/src/__tests__/bundle-request-middleware.test.ts

@@ -0,0 +1,123 @@
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import type { Config as HarnessConfig } from '@react-native-harness/config';
+import type { Reporter, ReportableEvent } from '../reporter.js';
+import { getBundleRequestObserverMiddleware } from '../middlewares/bundle-request-middleware.js';
+import { HARNESS_REQUEST_KIND_HEADER } from '../request-kind.js';
+
+const createReporter = () => {
+  const events: ReportableEvent[] = [];
+
+  const reporter: Reporter = {
+    addListener: vi.fn(),
+    removeListener: vi.fn(),
+    clearAllListeners: vi.fn(),
+    emit: (event) => {
+      events.push(event);
+    },
+  };
+
+  return { events, reporter };
+};
+
+const createProjectRoot = () => {
+  const projectRoot = fs.mkdtempSync(
+    path.join(os.tmpdir(), 'rn-harness-bundle-request-')
+  );
+  tempDirs.push(projectRoot);
+  fs.writeFileSync(path.join(projectRoot, 'index.js'), 'module.exports = {};');
+  return projectRoot;
+};
+
+const tempDirs: string[] = [];
+
+afterEach(() => {
+  for (const tempDir of tempDirs.splice(0)) {
+    fs.rmSync(tempDir, { recursive: true, force: true });
+  }
+});
+
+const createHarnessConfig = (): HarnessConfig =>
+  ({
+    entryPoint: './index.js',
+  }) as HarnessConfig;
+
+describe('bundle request observer middleware', () => {
+  it('emits app-originated entry bundle requests', () => {
+    const { events, reporter } = createReporter();
+    const middleware = getBundleRequestObserverMiddleware(
+      createProjectRoot(),
+      createHarnessConfig(),
+      reporter
+    );
+    const next = vi.fn();
+
+    middleware(
+      {
+        headers: {},
+        url: '/index.bundle?platform=ios&dev=true',
+      } as never,
+      {} as never,
+      next
+    );
+
+    expect(events).toEqual([
+      expect.objectContaining({
+        type: 'bundle_request_observed',
+        platform: 'ios',
+        requestKind: 'app',
+        url: '/index.bundle?platform=ios&dev=true',
+      }),
+    ]);
+    expect(next).toHaveBeenCalledTimes(1);
+  });
+
+  it('tags prewarm requests using the Harness header', () => {
+    const { events, reporter } = createReporter();
+    const middleware = getBundleRequestObserverMiddleware(
+      createProjectRoot(),
+      createHarnessConfig(),
+      reporter
+    );
+
+    middleware(
+      {
+        headers: {
+          [HARNESS_REQUEST_KIND_HEADER]: 'prewarm',
+        },
+        url: '/index.bundle?platform=android',
+      } as never,
+      {} as never,
+      vi.fn()
+    );
+
+    expect(events).toEqual([
+      expect.objectContaining({
+        platform: 'android',
+        requestKind: 'prewarm',
+      }),
+    ]);
+  });
+
+  it('ignores non-entry bundle requests', () => {
+    const { events, reporter } = createReporter();
+    const middleware = getBundleRequestObserverMiddleware(
+      createProjectRoot(),
+      createHarnessConfig(),
+      reporter
+    );
+
+    middleware(
+      {
+        headers: {},
+        url: '/other.bundle?platform=ios',
+      } as never,
+      {} as never,
+      vi.fn()
+    );
+
+    expect(events).toEqual([]);
+  });
+});