hmon: add C++ HMON unit tests

- Rename previous test to `integrated_test`.
- Reimplement Rust unit tests into C++.

Author: arkjedrz

src/health_monitoring_lib/BUILD

@@ -160,8 +160,13 @@ rust_test(
 cc_gtest_unit_test(
     name = "cpp_tests",
     srcs = [
+        "cpp/tests/deadline_monitor_test.cpp",
         "cpp/tests/health_monitor_test.cpp",
+        "cpp/tests/heartbeat_monitor_test.cpp",
+        "cpp/tests/integrated_test.cpp",
         "cpp/tests/log_init.cpp",
+        "cpp/tests/logic_monitor_test.cpp",
+        "cpp/tests/time_range_test.cpp",
     ],
     linkopts = select({
         "@platforms//os:qnx": ["-lsocket"],

src/health_monitoring_lib/cpp/tests/deadline_monitor_test.cpp

@@ -0,0 +1,111 @@
+/********************************************************************************
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Apache License Version 2.0 which is available at
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ ********************************************************************************/
+
+#include "score/hm/deadline/deadline_monitor.h"
+#include "score/hm/health_monitor.h"
+#include <gtest/gtest.h>
+
+using namespace score::hm;
+using namespace score::hm::deadline;
+
+TEST(DeadlineMonitorBuilder, New_Succeeds)
+{
+    DeadlineMonitorBuilder deadline_monitor_builder;
+}
+
+TEST(DeadlineMonitorBuilder, AddDeadline_Succeeds)
+{
+    using namespace std::chrono_literals;
+    DeadlineTag deadline_tag{"deadline"};
+    TimeRange range{50ms, 150ms};
+    auto deadline_monitor_builder{DeadlineMonitorBuilder{}.add_deadline(deadline_tag, range)};
+}
+
+class DeadlineMonitorFixture : public ::testing::Test
+{
+  protected:
+    std::optional<DeadlineMonitor> deadline_monitor_;
+
+    void SetUp() override
+    {
+        // Monitor must be obtained from HMON.
+        // Initialize deadline monitor builder.
+        using namespace std::chrono_literals;
+        MonitorTag deadline_monitor_tag{"deadline_monitor"};
+        DeadlineTag deadline_tag{"deadline"};
+        TimeRange range{50ms, 150ms};
+        auto deadline_monitor_builder{DeadlineMonitorBuilder{}.add_deadline(deadline_tag, range)};
+
+        // Build HMON, including deadline monitor.
+        auto hmon_build_result{HealthMonitorBuilder{}
+                                   .add_deadline_monitor(deadline_monitor_tag, std::move(deadline_monitor_builder))
+                                   .build()};
+        ASSERT_TRUE(hmon_build_result.has_value());
+        auto hmon{std::move(hmon_build_result.value())};
+
+        // Get deadline monitor.
+        auto get_deadline_monitor_result{hmon.get_deadline_monitor(deadline_monitor_tag)};
+        ASSERT_TRUE(get_deadline_monitor_result.has_value());
+        deadline_monitor_ = std::move(get_deadline_monitor_result.value());
+    }
+};
+
+TEST_F(DeadlineMonitorFixture, GetDeadline_Succeeds)
+{
+    // Get deadline.
+    auto get_deadline_result{deadline_monitor_->get_deadline(DeadlineTag{"deadline"})};
+    ASSERT_TRUE(get_deadline_result.has_value());
+}
+
+TEST_F(DeadlineMonitorFixture, GetDeadline_Unknown)
+{
+    // Get deadline.
+    auto get_deadline_result{deadline_monitor_->get_deadline(DeadlineTag{"unknown"})};
+    ASSERT_FALSE(get_deadline_result.has_value());
+    ASSERT_EQ(get_deadline_result.error(), Error::NotFound);
+}
+
+class DeadlineFixture : public DeadlineMonitorFixture
+{
+};
+
+TEST_F(DeadlineFixture, Start_Succeeds)
+{
+    // Get deadline.
+    DeadlineTag deadline_tag{"deadline"};
+    auto get_deadline_result{deadline_monitor_->get_deadline(deadline_tag)};
+    ASSERT_TRUE(get_deadline_result.has_value());
+    auto deadline{std::move(get_deadline_result.value())};
+
+    // Try to start and stop deadline.
+    auto deadline_start_result{deadline.start()};
+    ASSERT_TRUE(deadline_start_result.has_value());
+    auto deadline_handle{std::move(deadline_start_result.value())};
+
+    deadline_handle.stop();
+}
+
+TEST_F(DeadlineFixture, Start_AlreadyRunning)
+{
+    // Get deadline.
+    DeadlineTag deadline_tag{"deadline"};
+    auto get_deadline_result{deadline_monitor_->get_deadline(deadline_tag)};
+    ASSERT_TRUE(get_deadline_result.has_value());
+    auto deadline{std::move(get_deadline_result.value())};
+
+    // Try to start the deadline twice.
+    deadline.start();
+    auto deadline_start_result{deadline.start()};
+    ASSERT_FALSE(deadline_start_result.has_value());
+    ASSERT_EQ(deadline_start_result.error(), Error::Failed);
+}