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/SafeSignal.cpp

@@ -0,0 +1,63 @@
+#define CATCH_CONFIG_RUNNER
+#include "util/SafeSignal.hpp"
+
+#include <glibmm.h>
+
+#include <catch2/catch.hpp>
+#include <thread>
+
+#include "GlibTestsFixture.hpp"
+
+using namespace waybar;
+/**
+ * Basic sanity test for SafeSignal:
+ * check that type deduction works, events are delivered and the order is right
+ * Running this with -fsanitize=thread should not fail
+ */
+TEST_CASE_METHOD(GlibTestsFixture, "SafeSignal basic functionality", "[signal][thread][util]") {
+  const int NUM_EVENTS = 100;
+  int       count = 0;
+  int       last_value = 0;
+
+  SafeSignal<int, std::string> test_signal;
+
+  const auto  main_tid = std::this_thread::get_id();
+  std::thread producer;
+
+  // timeout the test in 500ms
+  Glib::signal_timeout().connect_once([]() { throw std::runtime_error("Test timed out"); }, 500);
+
+  test_signal.connect([&](auto val, auto str) {
+    static_assert(std::is_same<int, decltype(val)>::value);
+    static_assert(std::is_same<std::string, decltype(str)>::value);
+    // check that we're in the same thread as the main loop
+    REQUIRE(std::this_thread::get_id() == main_tid);
+    // check event order
+    REQUIRE(val == last_value + 1);
+
+    last_value = val;
+    if (++count >= NUM_EVENTS) {
+      this->quit();
+    };
+  });
+
+  run([&]() {
+    // check that events from the same thread are delivered and processed synchronously
+    test_signal.emit(1, "test");
+    REQUIRE(count == 1);
+
+    // start another thread and generate events
+    producer = std::thread([&]() {
+      for (auto i = 2; i <= NUM_EVENTS; ++i) {
+        test_signal.emit(i, "test");
+      }
+    });
+  });
+  producer.join();
+  REQUIRE(count == NUM_EVENTS);
+}
+
+int main(int argc, char* argv[]) {
+  Glib::init();
+  return Catch::Session().run(argc, argv);
+}