diff --git a/packages/react-native/ReactCommon/cxxreact/tests/RAMBundleRegistryTest.cpp b/packages/react-native/ReactCommon/cxxreact/tests/RAMBundleRegistryTest.cpp
new file mode 100644
index 000000000000..53c491319031
--- /dev/null
+++ b/packages/react-native/ReactCommon/cxxreact/tests/RAMBundleRegistryTest.cpp
@@ -0,0 +1,146 @@
+/*
+ * 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.
+ */
+
+#include <gtest/gtest.h>
+
+#include <memory>
+#include <stdexcept>
+#include <string>
+
+#include <cxxreact/RAMBundleRegistry.h>
+
+// RAMBundleRegistry.h compiles to an empty header when RCT_REMOVE_LEGACY_ARCH
+// is defined (e.g. the iOS build configs), so this guard is required for the
+// test file to compile across all platforms.
+#ifndef RCT_REMOVE_LEGACY_ARCH
+
+namespace facebook::react {
+namespace {
+
+// Minimal JSModulesUnbundle test double that always returns a preconfigured
+// module and records the last module ID it was asked for.
+class FakeModulesUnbundle : public JSModulesUnbundle {
+ public:
+  explicit FakeModulesUnbundle(Module module) : module_(std::move(module)) {}
+
+  Module getModule(uint32_t moduleId) const override {
+    lastRequestedModuleId = moduleId;
+    return module_;
+  }
+
+  mutable uint32_t lastRequestedModuleId = 0;
+
+ private:
+  Module module_;
+};
+
+std::unique_ptr<FakeModulesUnbundle> makeUnbundle(
+    std::string name,
+    std::string code) {
+  return std::make_unique<FakeModulesUnbundle>(JSModulesUnbundle::Module{
+      .name = std::move(name), .code = std::move(code)});
+}
+
+} // namespace
+
+TEST(RAMBundleRegistryTest, getModuleFromMainBundleReturnsModuleUnchanged) {
+  auto mainBundle = makeUnbundle("mainModule", "main code");
+  auto* mainBundleRaw = mainBundle.get();
+  RAMBundleRegistry registry(std::move(mainBundle));
+
+  auto module = registry.getModule(RAMBundleRegistry::MAIN_BUNDLE_ID, 42);
+
+  // The main bundle's module is returned verbatim, with no "seg-" prefixing.
+  EXPECT_EQ(module.name, "mainModule");
+  EXPECT_EQ(module.code, "main code");
+  EXPECT_EQ(mainBundleRaw->lastRequestedModuleId, 42u);
+}
+
+TEST(RAMBundleRegistryTest, getModuleFromSecondaryBundlePrefixesName) {
+  std::string capturedPath;
+  auto factory =
+      [&capturedPath](std::string path) -> std::unique_ptr<JSModulesUnbundle> {
+    capturedPath = std::move(path);
+    return makeUnbundle("segModule", "seg code");
+  };
+
+  RAMBundleRegistry registry(makeUnbundle("main", "main"), factory);
+  registry.registerBundle(7, "/bundles/seg7.js");
+
+  auto module = registry.getModule(7, 3);
+
+  // The factory is resolved using the path registered for bundle 7 and the
+  // resulting module name is namespaced with the bundle ID.
+  EXPECT_EQ(capturedPath, "/bundles/seg7.js");
+  EXPECT_EQ(module.name, "seg-7_segModule");
+  EXPECT_EQ(module.code, "seg code");
+}
+
+TEST(RAMBundleRegistryTest, getModuleWithoutFactoryThrows) {
+  RAMBundleRegistry registry(makeUnbundle("main", "main"));
+  registry.registerBundle(1, "/bundles/seg1.js");
+
+  EXPECT_THROW(
+      {
+        try {
+          registry.getModule(1, 0);
+        } catch (const std::runtime_error& e) {
+          EXPECT_NE(
+              std::string(e.what()).find("register factory function"),
+              std::string::npos);
+          throw;
+        }
+      },
+      std::runtime_error);
+}
+
+TEST(RAMBundleRegistryTest, getModuleWithUnregisteredPathThrows) {
+  bool factoryCalled = false;
+  auto factory =
+      [&factoryCalled](std::string) -> std::unique_ptr<JSModulesUnbundle> {
+    factoryCalled = true;
+    return nullptr;
+  };
+  RAMBundleRegistry registry(makeUnbundle("main", "main"), factory);
+
+  EXPECT_THROW(
+      {
+        try {
+          registry.getModule(9, 0);
+        } catch (const std::runtime_error& e) {
+          EXPECT_NE(std::string(e.what()).find("path"), std::string::npos);
+          throw;
+        }
+      },
+      std::runtime_error);
+  // The factory must not run when the bundle path was never registered.
+  EXPECT_FALSE(factoryCalled);
+}
+
+TEST(RAMBundleRegistryTest, secondaryBundleCreatedOnceAndCached) {
+  int factoryCallCount = 0;
+  auto factory =
+      [&factoryCallCount](std::string) -> std::unique_ptr<JSModulesUnbundle> {
+    ++factoryCallCount;
+    return makeUnbundle("segModule", "seg code");
+  };
+  RAMBundleRegistry registry(makeUnbundle("main", "main"), factory);
+  registry.registerBundle(4, "/bundles/seg4.js");
+
+  auto first = registry.getModule(4, 1);
+  auto second = registry.getModule(4, 2);
+
+  // The factory is invoked lazily only on the first access; the constructed
+  // bundle is cached and reused for subsequent module lookups.
+  EXPECT_EQ(factoryCallCount, 1);
+  EXPECT_EQ(first.name, "seg-4_segModule");
+  EXPECT_EQ(second.name, "seg-4_segModule");
+}
+
+} // namespace facebook::react
+
+#endif // RCT_REMOVE_LEGACY_ARCH