diff --git a/include/loki/common/pddl/garbage_collected_factory.hpp b/include/loki/common/pddl/garbage_collected_factory.hpp
index d319101d..5aca59ed 100644
--- a/include/loki/common/pddl/garbage_collected_factory.hpp
+++ b/include/loki/common/pddl/garbage_collected_factory.hpp
@@ -18,6 +18,7 @@
 #ifndef LOKI_INCLUDE_LOKI_COMMON_PDDL_GARBAGE_COLLECTED_FACTORY_HPP_
 #define LOKI_INCLUDE_LOKI_COMMON_PDDL_GARBAGE_COLLECTED_FACTORY_HPP_
 
+#include <cassert>
 #include <unordered_map>
 #include <unordered_set>
 #include <memory>
diff --git a/tests/common/pddl/garbage_collected_factory.cpp b/tests/common/pddl/garbage_collected_factory.cpp
index 6b02b93a..323c18a8 100644
--- a/tests/common/pddl/garbage_collected_factory.cpp
+++ b/tests/common/pddl/garbage_collected_factory.cpp
@@ -16,6 +16,7 @@
  */
 
 #include "../../../include/loki/common/pddl/garbage_collected_factory.hpp"
+#include "../../../include/loki/common/hash.hpp"
 #include "../../../include/loki/domain/pddl/object.hpp"
 
 #include <gtest/gtest.h>
@@ -24,33 +25,67 @@
 
 
 namespace loki::domain::tests {
-/*
-class Object {
+
+/// @brief A type to avoid friending in the pddl::Object since this class is not used.
+class ObjectImpl {
 private:
     int m_identifier;
     std::string m_name;
 
-    Object(int identifier, std::string name) : m_identifier(identifier), m_name(std::move(name)) { }
+    ObjectImpl(int identifier, std::string name) : m_identifier(identifier), m_name(std::move(name)) { }
 
     template<typename... Ts>
-    friend class GarbageCollectedFactory;
+    friend class loki::GarbageCollectedFactory;
 
 public:
+    bool operator==(const ObjectImpl& other) const {
+        return m_name == other.m_name;
+    }
+
+    size_t hash() const {
+        return hash_combine(m_name);
+    }
+
     int get_identifier() const { return m_identifier; }
     const std::string& get_name() const { return m_name; }
 };
 
+using Object = std::shared_ptr<ObjectImpl>;
+
+}
+
+
+namespace std {
+    template<>
+    struct hash<loki::domain::tests::ObjectImpl> {
+        size_t operator()(const loki::domain::tests::ObjectImpl& object) const {
+            return object.hash();
+        }
+    };
+}
+
+
+namespace loki::domain::tests {
+
 TEST(LokiTests, GarbageCollectedFactoryTest) {
-    GarbageCollectedFactory<Object> factory;
-    EXPECT_EQ(factory.size<Object>(), 0);
+    GarbageCollectedFactory<ObjectImpl> factory;
+    EXPECT_EQ(factory.size<ObjectImpl>(), 0);
 
     {
-        const auto object_0 = factory.get_or_create<Object>("object_0");
-        EXPECT_EQ(factory.size<Object>(), 1);
-        EXPECT_EQ(object_0->get_name(), "object_0");
-        // destructor is called
+        const auto object_0_0 = factory.get_or_create<ObjectImpl>("object_0");
+        EXPECT_EQ(factory.size<ObjectImpl>(), 1);
+        EXPECT_EQ(object_0_0->get_name(), "object_0");
+
+        const auto object_0_1 = factory.get_or_create<ObjectImpl>("object_0");
+        EXPECT_EQ(factory.size<ObjectImpl>(), 1);
+        EXPECT_EQ(object_0_0, object_0_1);
+
+        const auto object_1 = factory.get_or_create<ObjectImpl>("object_1");
+        EXPECT_EQ(factory.size<ObjectImpl>(), 2);
+
+        // destructors are called
     }
-    EXPECT_EQ(factory.size<Object>(), 0);
+    EXPECT_EQ(factory.size<ObjectImpl>(), 0);
 }
-*/
+
 }
diff --git a/tests/common/pddl/persistent_factory.cpp b/tests/common/pddl/persistent_factory.cpp
index 17da35d7..1e170160 100644
--- a/tests/common/pddl/persistent_factory.cpp
+++ b/tests/common/pddl/persistent_factory.cpp
@@ -32,10 +32,15 @@ TEST(LokiTests, PersistentFactoryTest) {
     EXPECT_EQ(factory.size(), 1);
     EXPECT_EQ(object_0_0->get_identifier(), 0);
     EXPECT_EQ(object_0_0->get_name(), "object_0");
+
     const auto object_0_1 = factory.get_or_create<pddl::ObjectImpl>("object_0");
     EXPECT_EQ(factory.size(), 1);
     EXPECT_EQ(object_0_0, object_0_1);
 
+    const auto object_1 = factory.get_or_create<pddl::ObjectImpl>("object_1");
+    EXPECT_EQ(factory.size(), 2);
+    EXPECT_NE(object_0_0, object_1);
+
 }
 
 }