Move ReactNativeTester to react-native repo

packages/react-native/src/private/__tests__/ReactNativeTester.js

@@ -0,0 +1,46 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ */
+
+import type {MixedElement} from 'react';
+
+import ReactFabric from '../../../Libraries/Renderer/shims/ReactFabric';
+
+let globalSurfaceIdCounter = 1;
+
+class Root {
+  #surfaceId: number;
+  #hasRendered: boolean = false;
+
+  constructor() {
+    this.#surfaceId = globalSurfaceIdCounter;
+    globalSurfaceIdCounter += 10;
+  }
+
+  render(element: MixedElement) {
+    if (!this.#hasRendered) {
+      global.$$JSTesterModuleName$$.startSurface(this.#surfaceId);
+      this.#hasRendered = true;
+    }
+    ReactFabric.render(element, this.#surfaceId);
+  }
+
+  destroy() {
+    // TODO: check for leaks.
+    global.$$JSTesterModuleName$$.stopSurface(this.#surfaceId);
+  }
+
+  // TODO: add an API to check if all surfaces were deallocated when tests are finished.
+}
+
+// TODO: Add option to define surface props and pass it to startSurface
+// Surfacep rops: concurrentRoot, surfaceWidth, surfaceHeight, layoutDirection, pointScaleFactor.
+export function createRoot(): Root {
+  return new Root();
+}