Add unit tests for ObjectCache.

ruby/ext/google/protobuf_c/protobuf.c

@@ -272,6 +272,8 @@ static void ObjectCache_Init(VALUE protobuf) {
 
   weak_obj_cache = rb_class_new_instance(0, NULL, cache_class);
   rb_const_set(protobuf, rb_intern("OBJECT_CACHE"), weak_obj_cache);
+  rb_const_set(protobuf, rb_intern("SIZEOF_LONG"), INT2NUM(SIZEOF_LONG));
+  rb_const_set(protobuf, rb_intern("SIZEOF_VALUE"), INT2NUM(SIZEOF_VALUE));
 }
 
 VALUE ObjectCache_TryAdd(const void *key, VALUE val) {

ruby/tests/BUILD.bazel

@@ -76,6 +76,16 @@ ruby_test(
     ],
 )
 
+ruby_test(
+    name = "object_cache_test",
+    srcs = ["object_cache_test.rb"],
+    deps = [
+        "//ruby:protobuf",
+        "//ruby:test_ruby_protos",
+        "@protobuf_bundle//:test-unit",
+    ],
+)
+
 ruby_test(
     name = "repeated_field_test",
     srcs = ["repeated_field_test.rb"],

ruby/tests/object_cache_test.rb

@@ -0,0 +1,41 @@
+require 'google/protobuf'
+require 'test/unit'
+
+class ObjectCacheTest < Test::Unit::TestCase
+  def test_correct_implementation_for_platform
+    if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new('2.7.0') and Google::Protobuf::SIZEOF_LONG >= Google::Protobuf::SIZEOF_VALUE
+      assert_instance_of Google::Protobuf::ObjectCache, Google::Protobuf::OBJECT_CACHE
+    else
+      assert_instance_of Google::Protobuf::LegacyObjectCache, Google::Protobuf::OBJECT_CACHE
+    end
+  end
+
+  def test_try_add_returns_existing_value
+    cache = Google::Protobuf::OBJECT_CACHE.class.new
+    key = 0xdeadbeefdeadbeef
+    first_value = 42
+    second_value = 43
+    assert_same first_value, cache.try_add(key, first_value)
+    assert_same first_value, cache.get(key)
+    assert_same first_value, cache.try_add(key, second_value)
+    assert_same first_value, cache.get(key)
+  end
+
+  def test_multithreaded_access
+    cache = Google::Protobuf::OBJECT_CACHE.class.new
+    key = 0xdeadbeefdeadbeef
+    threads = []
+
+    100.times do |i|
+      threads[i] = Thread.new {
+        Thread.current["result"] = cache.try_add(key, i)
+      }
+    end
+
+    results = {}
+
+    threads.each_with_index {|t, i | t.join; results[i] = t["result"] }
+    assert_equal 100, results.size
+    assert_equal 1, results.values.uniq.size
+  end
+end