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/meson.build

@@ -2,6 +2,7 @@ test_inc = include_directories('../include')
 test_dep = [
     catch2,
     fmt,
+    gtkmm,
     jsoncpp,
     spdlog,
 ]
@@ -14,8 +15,21 @@ config_test = executable(
     include_directories: test_inc,
 )
 
+safesignal_test = executable(
+    'safesignal_test',
+    'SafeSignal.cpp',
+    dependencies: test_dep,
+    include_directories: test_inc,
+)
+
 test(
     'Configuration test',
     config_test,
     workdir: meson.source_root(),
 )
+
+test(
+    'SafeSignal test',
+    safesignal_test,
+    workdir: meson.source_root(),
+)