Add test utilities for C++ and Java

Summary:
@public

Test utility on top of the new event system that maintains a counter of instantiated nodes. Meant to replace the global node counter.

Reviewed By: SidharthGuglani

Differential Revision: D15174855

fbshipit-source-id: 6998472f95a09b8da652257a26596164bdcf43d6

testutil/jni.cpp

@@ -0,0 +1,38 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the LICENSE
+ * file in the root directory of this source tree.
+ */
+#include <fb/fbjni.h>
+#include <yoga/testutil/testutil.h>
+
+using namespace facebook;
+
+namespace {
+
+void startCountingNodes(jni::alias_ref<jclass>) {
+  yoga::test::TestUtil::startCountingNodes();
+}
+
+jint nodeCount(jni::alias_ref<jclass>) {
+  return yoga::test::TestUtil::nodeCount();
+}
+
+jint stopCountingNodes(jni::alias_ref<jclass>) {
+  return yoga::test::TestUtil::stopCountingNodes();
+}
+
+} // namespace
+
+jint JNI_OnLoad(JavaVM* vm, void*) {
+  return jni::initialize(vm, [] {
+    jni::registerNatives(
+        "com/facebook/yoga/TestUtil",
+        {
+            makeNativeMethod("startCountingNodes", startCountingNodes),
+            makeNativeMethod("nodeCount", nodeCount),
+            makeNativeMethod("stopCountingNodes", stopCountingNodes),
+        });
+  });
+}