Add JVM tests for the Android pull model plumbing (#57583)

Summary:
Pull Request resolved: #57583

Robolectric tests for the notification path: a notification pulls synchronously on the UI thread; one pull item is enqueued per notification and dispatched in order (redundant pulls no-op in C++); no binding is a clean no-op. Adds `ShadowFabricUIManagerBinding` and `ShadowPerformanceTracer` shadows.

## Changelog:
[Internal] - Add JVM tests for the Android pull-model plumbing

Reviewed By: cortinico

Differential Revision: D112309051

Author: Bartlomiej Bloniarz

packages/react-native/ReactAndroid/src/test/java/com/facebook/react/fabric/FabricUIManagerPullModelTest.kt

@@ -0,0 +1,108 @@
+/*
+ * 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.
+ */
+
+@file:Suppress("DEPRECATION")
+
+package com.facebook.react.fabric
+
+import com.facebook.react.bridge.ReactApplicationContext
+import com.facebook.react.bridge.ReactTestHelper
+import com.facebook.react.internal.featureflags.ReactNativeFeatureFlagsForTests
+import com.facebook.react.uimanager.ViewManagerRegistry
+import com.facebook.testutils.fakes.FakeBatchEventDispatchedListener
+import com.facebook.testutils.shadows.ShadowFabricUIManagerBinding
+import com.facebook.testutils.shadows.ShadowNativeLoader
+import com.facebook.testutils.shadows.ShadowPerformanceTracer
+import com.facebook.testutils.shadows.ShadowSoLoader
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+import org.robolectric.shadow.api.Shadow
+
+/**
+ * Tests for the pull-model notification path: [FabricUIManager.onTransactionAvailable] enqueues a
+ * PullTransactionMountItem that asks the (shadowed, JNI-backed) [FabricUIManagerBinding] to pull
+ * and apply the surface's pending transaction.
+ *
+ * The Robolectric test thread is the UI thread, so a notification posted from it dispatches the
+ * queued mount items synchronously; notifications posted from a background thread stay queued until
+ * the next UI-thread dispatch (in production, the dispatcher's frame callback).
+ */
+@RunWith(RobolectricTestRunner::class)
+@Config(
+    shadows =
+        [
+            ShadowSoLoader::class,
+            ShadowNativeLoader::class,
+            ShadowPerformanceTracer::class,
+            ShadowFabricUIManagerBinding::class,
+        ]
+)
+class FabricUIManagerPullModelTest {
+
+  private lateinit var reactContext: ReactApplicationContext
+  private lateinit var underTest: FabricUIManager
+  private lateinit var binding: FabricUIManagerBinding
+  private lateinit var shadowBinding: ShadowFabricUIManagerBinding
+
+  @Before
+  fun setup() {
+    ReactNativeFeatureFlagsForTests.setUp()
+    reactContext = ReactTestHelper.createCatalystContextForTest()
+    underTest =
+        FabricUIManager(
+            reactContext,
+            ViewManagerRegistry(emptyList()),
+            FakeBatchEventDispatchedListener(),
+        )
+    binding = FabricUIManagerBinding()
+    shadowBinding = Shadow.extract(binding)
+    underTest.setBinding(binding)
+  }
+
+  private fun runOnBackgroundThread(block: () -> Unit) {
+    var error: Throwable? = null
+    val thread = Thread {
+      try {
+        block()
+      } catch (t: Throwable) {
+        error = t
+      }
+    }
+    thread.start()
+    thread.join()
+    error?.let { throw it }
+  }
+
+  @Test
+  fun onTransactionAvailable_onUiThread_pullsSynchronously() {
+    underTest.onTransactionAvailable(1)
+
+    assertThat(shadowBinding.pulledSurfaceIds).containsExactly(1)
+  }
+
+  @Test
+  fun onTransactionAvailable_enqueuesOnePullPerNotification() {
+    // Mirrors iOS: one transaction block per commit, in notification order. Redundant pulls
+    // (revisions already consumed by an earlier accumulating pull) no-op in C++, not here.
+    runOnBackgroundThread {
+      underTest.onTransactionAvailable(1)
+      underTest.onTransactionAvailable(2)
+      underTest.onTransactionAvailable(1)
+    }
+    // Notifications from a background (commit) thread are queued, not dispatched.
+    assertThat(shadowBinding.pulledSurfaceIds).isEmpty()
+
+    // The next UI-thread dispatch drains them in order.
+    underTest.onTransactionAvailable(3)
+
+    assertThat(shadowBinding.pulledSurfaceIds).containsExactly(1, 2, 1, 3)
+  }
+}

packages/react-native/ReactAndroid/src/test/java/com/facebook/testutils/shadows/ShadowFabricUIManagerBinding.kt

@@ -0,0 +1,26 @@
+/*
+ * 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.
+ */
+
+package com.facebook.testutils.shadows
+
+import org.robolectric.annotation.Implementation
+import org.robolectric.annotation.Implements
+
+/**
+ * [FabricUIManagerBinding] is JNI-backed and Mockito can't mock native methods, so shadow the
+ * methods tests need instead. The binding class is `internal`, so it is referenced by name via
+ * [Implements.className] rather than a compile-time class literal.
+ */
+@Implements(className = "com.facebook.react.fabric.FabricUIManagerBinding")
+class ShadowFabricUIManagerBinding {
+  val pulledSurfaceIds: MutableList<Int> = mutableListOf()
+
+  @Implementation
+  fun pullAndExecuteTransaction(surfaceId: Int) {
+    pulledSurfaceIds.add(surfaceId)
+  }
+}

packages/react-native/ReactAndroid/src/test/java/com/facebook/testutils/shadows/ShadowPerformanceTracer.kt

@@ -0,0 +1,24 @@
+/*
+ * 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.
+ */
+
+package com.facebook.testutils.shadows
+
+import com.facebook.react.internal.tracing.PerformanceTracer
+import kotlin.jvm.JvmStatic
+import org.robolectric.annotation.Implementation
+import org.robolectric.annotation.Implements
+
+/**
+ * [PerformanceTracer] is JNI-backed (react_tracingjni); shadow it so code paths that check
+ * [PerformanceTracer.isTracing] can run on the JVM. Tracing reports as disabled.
+ */
+@Implements(PerformanceTracer::class)
+class ShadowPerformanceTracer {
+  companion object {
+    @JvmStatic @Implementation fun isTracing(): Boolean = false
+  }
+}