feat: add support for proxy with no event loop thread

tests/integrationtests/DBusMethodsTests.cpp

@@ -272,3 +272,12 @@ TEST_F(SdbusTestObject, CannotSetGeneralMethodTimeoutWithLibsystemdVersionLessTh
     ASSERT_THROW(s_adaptorConnection->getMethodCallTimeout(), sdbus::Error);
 }
 #endif
+
+TEST_F(SdbusTestObject, CanCallMethodSynchronouslyWithoutAnEventLoopThread)
+{
+    auto proxy = std::make_unique<TestProxy>(BUS_NAME, OBJECT_PATH, sdbus::dont_run_event_loop_thread);
+
+    auto multiplyRes = proxy->multiply(INT64_VALUE, DOUBLE_VALUE);
+
+    ASSERT_THAT(multiplyRes, Eq(INT64_VALUE * DOUBLE_VALUE));
+}

tests/integrationtests/TestProxy.cpp

@@ -39,6 +39,13 @@ TestProxy::TestProxy(std::string destination, std::string objectPath)
     registerProxy();
 }
 
+TestProxy::TestProxy(std::string destination, std::string objectPath, dont_run_event_loop_thread_t)
+    : ProxyInterfaces(std::move(destination), std::move(objectPath), dont_run_event_loop_thread)
+{
+    // It doesn't make sense to register any signals here since proxy upon a D-Bus connection with no event loop thread
+    // will not receive any incoming messages except replies to synchronous D-Bus calls.
+}
+
 TestProxy::TestProxy(sdbus::IConnection& connection, std::string destination, std::string objectPath)
     : ProxyInterfaces(connection, std::move(destination), std::move(objectPath))
 {

tests/integrationtests/TestProxy.h

@@ -73,6 +73,7 @@ class TestProxy final : public sdbus::ProxyInterfaces< org::sdbuscpp::integratio
 {
 public:
     TestProxy(std::string destination, std::string objectPath);
+    TestProxy(std::string destination, std::string objectPath, dont_run_event_loop_thread_t);
     TestProxy(sdbus::IConnection& connection, std::string destination, std::string objectPath);
     ~TestProxy();