test(util): add tests for SafeSignal

Add a fixture for writing tests that require interaction with Glib event
loop and a very basic test for SafeSignal.

test/GlibTestsFixture.hpp

@@ -0,0 +1,19 @@
+#pragma once
+#include <glibmm/main.h>
+/**
+ * Minimal Glib application to be used for tests that require Glib main loop
+ */
+class GlibTestsFixture : public sigc::trackable {
+ public:
+  GlibTestsFixture() : main_loop_{Glib::MainLoop::create()} {}
+
+  void run(std::function<void()> fn) {
+    Glib::signal_idle().connect_once(fn);
+    main_loop_->run();
+  }
+
+  void quit() { main_loop_->quit(); }
+
+ protected:
+  Glib::RefPtr<Glib::MainLoop> main_loop_;
+};