test: add tests for waybar_time formatter

test/meson.build

@@ -6,13 +6,21 @@ test_dep = [
     jsoncpp,
     spdlog,
 ]
-
-waybar_test = executable(
-    'waybar_test',
+test_src = files(
     'main.cpp',
     'SafeSignal.cpp',
     'config.cpp',
     '../src/config.cpp',
+)
+
+if tz_dep.found()
+  test_dep += tz_dep
+  test_src += files('waybar_time.cpp')
+endif
+
+waybar_test = executable(
+    'waybar_test',
+    test_src,
     dependencies: test_dep,
     include_directories: test_inc,
 )